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Home › Tutorials
Visual Basic & ADO Tutorial Level:
Rank:
(3 votes)
This tutorial describes how you can use ADO objects in VB6. Now days, almost any time you write full fledged database application you will want to use ADO. Along with this, as your applications become more and more complex you will probably not want to rely on Visual Basic's data controls, but instead use the ADO objects directly. Read on to find out exactly how this can be done.
Originally Written By TheVBProgramer TheVBProgramer..
The "Alphabet Soup" of Database Access
Prior to VB6 and the introduction of ADO (ActiveX Data Objects), VB programmers would generally use DAO (Data Access Objects) to interact with local databases such as MS Access and use RDO (Remote Data Objects) to interact with client/server databases such as Oracle and SQL Server. The concept behind Visual Basic ADO was Universal Data Access (UDA), where one database access method could be used for any data source; it was designed to replace both DAO and RDO. DAO remains a viable technology for interacting with MS Access databases as it is faster than ADO for that purpose; however, ADO is more flexible – using ADO, one could develop a prototype database application using MS Access in the back-end, and with a "flick of the wrist" (i.e., with very little coding changes) "upsize" that same application to use Oracle or SQL Server. As far as RDO is concerned, no new versions of it have been developed beyond the version that shipped with Visual Basic, and there are no future plans for it.
In the VB4 and VB5 worlds, RDO was the main method used to interact with client/server databases. RDO works perfectly fine with VB6, so when folks migrated their VB5 applications over to VB6, little or no coding changes were required. However, ADO is the preferred method of database access for new VB6 applications .
About this Tutorial
This tutorial presents three small sample applications using ADO. All three applications use a local MS Access database. The first sample application introduces the ADO Data Control (ADODC) which demonstrates a "quick and dirty" way to connect to a remote database. The second and third applications use ADO code: the second allows navigation and searching of a database table; the third allows navigation and updating on a database table. All three connect to an ODBC Data Source, which must be set up through the Windows Control Panel. How to do this is described below.
Note: If you have previously set up a DSN for the Biblio database as described in the previous topic on RDO, you can skip the section on setting up an ODBC data source and resume here here..
Setting Up an ODBC Data Source
Follow the steps below to set up an ODBC Data Source (this process is also called "setting up a DSN", where "DSN" stands for "Data Source Name"). These steps assume Windows 2000 for the operating system. On other versions of Windows, some steps may vary slightly.
•
Via Windows Control Panel , double-click on Administrative Tools , then Data Sources (ODBC) . The ODBC Data Source Administrator screen is displayed, as shown below. Click
on the System DSN tab.
•
Click the Add button. The Create New Data Source dialog box will appear. Select Microsoft Access Driver (*.mdb) from the list and click the Finish button.
•
The ODBC Microsoft Access Setup dialog box will appear. For Data Source Name, type Biblio . If desired, you can type an entry for Description, but this is not required.
•
Click the Select button. The Select Database dialog box appears. On a default installation of VB6 or Visual Studio 6, the BIBLIO.MDB sample database should reside in the folder C:\Program Files\Microsoft Visual Studio\VB98 . Navigate to that folder, select
BIBLIO.MDB BIBLIO.MD B from the file list, and click OK.
Note: If VB was installed in a different location on your system, navigate to the appropriate folder. If you do not have the BIBLIO.MD BIBLIO.MDB B sample database file on your system at all, you can download it here here.. In that case, copy the file to the folder of your choice, and navigate to that folder to select the database for this step.
•
When you are returned to the ODBC Microsoft Access Setup screen, the database you selected should be reflected as shown below. Click OK to dismiss this screen.
•
When you are returned to the ODBC Data Source Administrator screen, the new DSN should appear as shown below. Click OK to dismiss this screen.
At this point, the Biblio database is ready to be used with RDO in the sample application.
Sample Application 1: Using the ADO Data Control (ADODC)
To build the first sample application, follow the steps below.
•
Start a new VB project, and from the Components dialog box (invoked from the Project -> Components menu), select Microsoft ADO Data Control 6.0 (SP x ) as shown below and
click OK.
The ADO Data Control should appear in your toolbox as shown below:
•
Put an ADO Data Control on your form, and set the properties as follows:
Property Name DataSourceName SQL
•
Value
adoBiblio Biblio select * from authors Now put three text boxes on the form, and set their Name, DataSource, and DataField DataField properties as follows:
•
Name
DataSource
DataField
txtAuthor txtAuID txtYearBorn
adoBiblio adoBiblio adoBiblio
Author Au_ID Year Born
Save and run the program. Notice how it works just like the other data control.
•
Now change the SQL property of the data control to select * from authors order by author and run the program again. Notice the difference.
•
Change the SQL property back to what it was and add three command buttons to the form, and set their Name and Caption properties as follows:
•
Name
Caption
cmdNameOrder cmdYearOrder cmdIDOrder
Order by Name Order by Year Order by ID
Put the following code in the cmdNameOrder_Click event:
adoBiblio.SQL = "select * from authors order by author" adoBiblio.Refresh
•
Put the following code in the cmdYearOrder_Click event:
adoBiblio.SQL = "select * from authors order by [year born]" adoBiblio.Refresh
•
Put the following code in the cmdIDOrder_Click event:
adoBiblio.SQL = "select * from authors order by au_id" adoBiblio.Refresh
•
Save and run the program and see what happens when you click the buttons.
A screen-shot of the sample app at run-time is shown below:
Download the project files for this sample application here here..
Sample Applications Applications 2 and 3: Using ADO Code
Note: If you have previously downloaded and set up a DSN for the Property database as described in the previous topic on RDO, you can skip the set up steps below and resume here here..
Sample applications 2 and 3 use a database called PROPERTY.MDB and can be downloaded here.. here
The Property database contains just one table called "Property". The columns of this table are defined as follows:
Column Name
Data Type
Notes
PROPNO
Number (Long Integer)
A number that uniquely identifies the property in the table. Should be treated as
the Primary Key (although it is not defined EMPNO
Number (Long Integer)
as such in the sample database). A number that identifies the real estate agent selling the property. In a real system, this would be the foreign key to the employee number in an Employee table (such a table is not present in the sample
ADDRESS CITY STATE ZIP NEIGHBORHOOD HOME_AGE
Text (20) Text (15) Text (2)
database). The street address of the property. The city where the property is located. The state where the property is located (2-
Text (5) Text (15)
character US state abbreviation). The zip code where the property is located. The descriptive name of the neighborhood
Number (Long Integer)
in which the property is located. Age in years of the home. (A better table design choice would be to have this field be the date in which the property was built and have the application compute the age
BEDS BATHS
Number (Long Integer) Number (Single)
based on the current date.) Number of bedrooms in the property. Number of bathrooms in the property (allows for a decimal value such as 2.5, indicating 2 ½ bathrooms – i.e. 2 full
FOOTAGE ASKING BID SALEPRICE
Number (Long Integer) Number (Long Integer)
bathrooms and 1 "powder room"). The footage of the property. Asking price of the property in whole
Number (Long Integer)
dollars. Bid amount of the potential buyer in whole
Number (Long Integer)
dollars. Sale price (amount the property actually
sold for) in whole dollars. Before coding or running sample application 2 or 3, you must set up an ODBC data source as was done for the previous sample application.
After downloading the file, move it to the folder of your choice. Then follow the exact same steps as before to set up the DSN, with these two exceptions:
(1) On the ODBC Microsoft Access Setup dialog box, type PropDB for the Data Source Name.
(2) In the Select Database dialog box, navigate to the location where you have placed the PROPERTY.MDB file.
Sample Application 2
To build Sample Application 2, start a new VB project and perform p erform the following steps.
•
From the Project -> References menu, check Microsoft ActiveX Data Objects 2. x x (where x is the highest version that you have on your system) and click OK.
•
This project uses the StatusBar control, so include the Microsoft Windows Common Controls 6.0 (SP6) from the Components dialog box, accessed from the Project -> Components menu.
•
Create the form shown below. The names of the text boxes in the top frame are shown in the form. Set the Enabled property of the frame to False, which will automatically disable all o f the textboxes within it, which is desired because this application does not allow updating of the data. The settings for the other controls are given below.
The navigation buttons have the following properties:
Name
Caption
cmdMoveFirst cmdMovePrevious cmdMoveNext cmdMoveLast
<< < > >>
The text box in the middle of the form has the following properties:
Name MultiLine Locked
The command buttons have the following properties:
txtCurrentQuery True True
Name
Caption
Enabled
cmdAllData cmdGetData
Reload All Records Run Query Now
True False
In the "Select Criteria" frame:
The check boxes are an array: a rray: Name
Caption
chkCriteria(0) chkCriteria(1) chkCriteria(2)
EmpNo City State
The labels are also an array: Name
Caption
Enabled
lblCriteria(0) lblCriteria(1) lblCriteria(2)
= Like Like
False False False
Name
Caption
Enabled
txtCriteria(0) txtCriteria(1) txtCriteria(2)
EmpNo City State
False False False
The textboxes are also an array:
Place the StatusBar on the form and set its Style property to 1 – sbrSimple.
2. Code the General Declarations section as shown below. Here, two ADO objects, ADODB.Connection and ADODB.Recordset , are defined at the form level.
The ADODB.Connection object represents an open connection to a data source and a specific database on that data source, or an allocated a llocated but as yet unconnected object, which can be used to subsequently establish a connection.
The ADODB.Recordset object represents the rows that result from running a query,
Option Explicit
Dim mobjADOConn As ADODB.Connection Dim mobjADORst As ADODB.Recordset Dim mstrSQL As String
3. Code the Form_Load event. Here, the connection object variable mobjADOConn is made available for use by setting it to a new instance of ADODB.Connection. Then, the ConnectionString property and the Open method of the ADODB.Connection object are
used.
The ConnectionString property takes a string with various arguments delimited by semicolons. When using a DSN as we are in this sample application, you typically need just the DSN name, the user id, and the password. The Open method then opens the connection to the database.
'---------------------------------------------------------------------------Private Sub Form_Load() '----------------------------------------------------------------------------
'set up the form and connect to the data source On Error GoTo LocalError 'center the form: Me.Top = (Screen.Height - Me.Height) / 2 Me.Left = (Screen.Width - Me.Width) / 2 ' Connect to the Property database: Set mobjADOConn = New ADODB.Connection mobjADOConn.ConnectionString = "DSN=PropDB;Uid=admin;Pwd=;" mobjADOConn.Open Call cmdAllData_Click
Exit Sub
LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
4. Code the cmdAllData_Cl cmdAllData_Click ick event, which sets or resets the ADODB.Recordset object with a query to display all the rows in the table. The opening of the recordset takes place in the OpenNewRecordset subprocedure, called from this event procedure.
'---------------------------------------------------------------------------Private Sub cmdAllData_Click() '----------------------------------------------------------------------------
On Error GoTo LocalError Dim lngX As Long
'select or reload the data to be displayed: mstrSQL = "select * from property" Call OpenNewRecordset 'load data into the text boxes Call DataLoad
' reset the state of the search criteria controls For lngX = 0 To 2 chkCriteria(lngX).Value = vbUnchecked Next Exit Sub
LocalError: MsgBox Err.Number & " - " & Err.Description
End Sub
5. Create the user-defined subprocedure OpenNewRecordset.
Here, the recordset object mobjADORst is made available for use by setting (or resetting) it to a new instance of ADODB.R ADODB.Recordset. ecordset.
The CursorLocation property is then set to the built-in constant adUseClient. The term "cursor" refers to the temporary rows of a recordset. The cursor location determines whether the cursor is stored on the client or the server, specified by the values adUseClient and adUseServer , respectively. Server-side cursor (adUseServer) is the default. There are
tradeoffs using both types of cursors. Client-side cursors can take a long time to build because the data must be pulled over to the client, but once built, traversing the cursor is usually very fast. Client-side cursors often support more features than server-side cursors (the reason this sample application is using a client-side cursor is because we want to use AbsolutePosition property later, which only works with a client-side cursor). On the other hand, server-side cursors usually build faster but often support fewer features that client-side cursors.
The Open method of the recordset is then executed. The Open method has the following syntax:
RecordsetObject .Open .Open Source, ActiveConnection, CursorType, LockType, Options
The Source argument is an optional variant that evaluates to a valid Command object, SQL statement, table name, stored procedure call, or filename of a persisted recordset.
The ActiveConnection argument is an optional variant that evaluates to a valid Connection object variable name or a string containing connection string parameters.
The CursorType argument is an optional value that determines the type of cursor that the provider should use when opening the recordset. The possible values and their descriptions are given below:
Value
Description
adOpenForwardOnly
(default) Used to open a forward-only cursor. Forward-only cursors create static snapshots of data. A recordset that uses a forward-only cursor is not directly updateable and can only be scrolled from beginning to end (i.e., "MoveNext" is the only "Move" method that can be used with this type of cursor). Forward-only cursors offer optimal performance in exchange for feature limitations. Forward-only Forward-only cursors
adOpenStatic
are sometimes referred to as firehose cursors. Used to open a static cursor. A static cursor is a static copy of the data in the data source. Once created, no changes made by other users propagate to the recordset; the recordset never changes. Note: Client side cursors (like the one used in this sample application) use only adOpenStatic for CursorTypes regardless of which CursorType you select.
adOpenDynamic
Used to open a dynamic cursor. A dynamic cursor is a "live" recordset, meaning that any and all additions, changes, and deletions by other users affect the recordset. Dynamic-cursor recordsets support all types of navigation, including bookmarks (if bookmarks are su pported by the provider). Dynamic cursors offer the most features of any cursor type,
adOpenKeyset
but at the expense of increased overhead. Used to open a keyset cursor. Keyset cursors are like dynamic cursors, except additions made by other users are not visible in the recordset.
The recordset is affected by changes and deletions, however. The LockType argument is an optional value that determines the type of locking that the provider should use when opening the recordset. The possible values and their descriptions are given below:
Value
Description
adLockReadOnly
(default) Specifies read-only locking. Records can be read, but data cannot be added, changed, or deleted. This is the locking method used with static cursors and forward-only cursors.
adLockPessimistic
Specifies pessimistic locking. The provider does what is necessary to ensure successful editing of records, usually by locking records at the
adLockOptimistic
data source immediately upon editing. Specifies optimistic optimistic locking. The provider locks records only when you
call the Update method, not when you start editing. adLockBatchOptimistic Specifies optimistic adLockBatchOptimistic optimistic batch locking. Records are locked locked in batch update mode, as opposed to immediate update mode. This option is required for client-side cursors. The Options argument is an optional Long value that indicates how the Source should be evaluated. The possible values and their descriptions are given below:
Value
Description
adCmdText
Indicates that the provider should evaluate CommandText as a textual
adCmdTable adCmdStoredProc
definition of a command. This options is used SQL statements. Indicates that the provider should evaluate CommandText as a table. Indicates that the provider should evaluate CommandText as a stored
adCmdUnknown
procedure. Indicates that the type of command in the CommandText argument is not known and that the provider should attempt to interpret it. Typically
adExecuteAsync adFetchAsync
results in poor performance. Indicates that the command should execute asynchronously. Indicates that the remaining rows after the initial quantity specified in
the CacheSize property should be fetched asynchronously. '---------------------------------------------------------------------------Private Sub OpenNewRecordset() '---------------------------------------------------------------------------Set mobjADORst = New ADODB.Recordset mobjADORst.CursorLocation = adUseClient mobjADORst.Open mstrSQL, mobjADOConn, adOpenStatic, , adCmdText
' display current query txtCurrentQuery.Text = mstrSQL
End Sub
6. Create the user-defined subprocedure DataLoad. This subprocedure gets the data from the recordset and puts each field into a text box. Data from the recordset is accessed via the Fields collection.
The Fields collection in ADO works identically to the Fields collection in DAO. A field can be referenced with or without specifying Fields, either by the field name in quotes or by its ordinal position in the resultset. The field can also be referenced with the bang (!) operator. All of the following would be valid ways of referencing the field "propno":
mobjADORst.Fields("propno") mobjADORst ("propno") mobjADORst.Fields(0) mobjADORst(0) mobjADORst!propno
'---------------------------------------------------------------------------Private Sub DataLoad() '---------------------------------------------------------------------------On Error GoTo LocalError
'copy the data from the recordset to the text boxes: txtPropNo.Text = mobjADORst.Fields("propno") txtEmpNo.Text = mobjADORst.Fields("empno") txtAddress.Text = mobjADORst.Fields("address") txtCity.Text = mobjADORst.Fields("city") txtState.Text = mobjADORst.Fields("state") txtZip.Text = mobjADORst.Fields("zip")
Call SetRecNum Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description
End Sub
7. Create the user-defined subprocedure SetRecNum. This sub displays the number of the current record at the bottom of the screen. The AbsolutePosition and RecordCount properties of the Recordset are used here.
The AbsolutePosition property specifies the current row in a recordset. Note: For AbsolutePosition AbsolutePositi on to return a valid value with Access (Jet) databases (like the one used in the sample application), the CursorLocation must be set to adUseClient. An invalid value (-1) will be returned if adUseClient a dUseClient is specified.
The RecordCount property the total number of rows in the recordset. Note: RecordCount will not return a valid value with all cursor types (for example, RecordCount will return -1 with a forward-only cursor.) To ensure a valid RecordCount value, use either adOpenKeyset or adOpenStatic as the CursorType for server side cursors or use a client side cursor.
'---------------------------------------------------------------------------Private Sub SetRecNum() '---------------------------------------------------------------------------StatusBar1.SimpleText = "row " & mobjADORst.AbsolutePosition _ & " of " & mobjADORst.RecordCount End Sub
8. Code the events for the navigation buttons as shown below, using the recordset "Move" methods to move to the first, last, next, or previous record, respectively.
'---------------------------------------------------------------------------Private Sub cmdMoveFirst_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MoveFirst Call DataLoad Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
'---------------------------------------------------------------------------Private Sub cmdMoveLast_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MoveLast Call DataLoad Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
'---------------------------------------------------------------------------Private Sub cmdMoveNext_Click()
'---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MoveNext If mobjADORst.EOF Then Beep mobjADORst.MoveLast End If Call DataLoad Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
'---------------------------------------------------------------------------Private Sub cmdMovePrevious_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MovePrevious If mobjADORst.BOF Then Beep mobjADORst.MoveFirst End If Call DataLoad Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description
End Sub
9. When one of the check boxes is clicked, the label and text box next to it should be enabled (or disabled, if clicking the check box unchecks it). Note also that the cmdGetData button (the one with the "Run Query Now" caption) should only be enabled if one of the checkboxes is checked.
'---------------------------------------------------------------------------Private Sub chkCriteria_Click(Index As Integer) '----------------------------------------------------------------------------
' disable the 'Run Query Now' button cmdGetData.Enabled = False
'when the user clicks on a check box, enable the label and text 'box that go with it. If chkCriteria(Index).Value = vbChecked Then txtCriteria(Index).Enabled = True lblCriteria(Index).Enabled = True txtCriteria(Index).SetFocus txtCriteria(Index).SelStart = 0 txtCriteria(Index).SelLength = Len(txtCriteria(Index).Text) ' enable the 'Run Query Now' button only if a box is checked. cmdGetData.Enabled = True Else txtCriteria(Index).Enabled = False lblCriteria(Index).Enabled = False End If End Sub
10. After the user has selected which fields to use and entered values in the text boxes, they click the cmdGetData button to create a new recordset with new data. Note that if the user selects (checks) a field, but does not enter search criteria in the corresponding textbox, an error message is generated and the query is not run.
'---------------------------------------------------------------------------Private Sub cmdGetData_Click() '----------------------------------------------------------------------------
'run the query that the user has created On Error GoTo LocalError
Dim blnFirstOne As Boolean blnFirstOne = True mstrSQL = "select * from property where " If chkCriteria(0).Value = vbChecked Then If (txtCriteria(0).Text = "") Or (Not IsNumeric(txtCriteria(0).Text)) Then MsgBox "Employee number is missing or non-numeric. Query not run.", _ vbExclamation, _ "ADO Example" Exit Sub End If blnFirstOne = False mstrSQL = mstrSQL & "empno = " & txtCriteria(0).Text End If If chkCriteria(1).Value = vbChecked Then If txtCriteria(1).Text = "" Then
MsgBox "City criteria is missing. Query not run.", _ vbExclamation, _ "ADO Example" Exit Sub End If If blnFirstOne = False Then mstrSQL = mstrSQL & " and" End If blnFirstOne = False mstrSQL = mstrSQL & " city like '" & txtCriteria(1).Text & "'" End If If chkCriteria(2).Value = vbChecked Then If txtCriteria(2).Text = "" Then MsgBox "State criteria is missing. Query not run.", _ vbExclamation, _ "ADO Example" Exit Sub End If If blnFirstOne = False Then mstrSQL = mstrSQL & " and" End If blnFirstOne = False mstrSQL = mstrSQL & " state like '" & txtCriteria(2).Text & "'" End If OpenNewRecordset 'make sure that the query did not return 0 rows: If mobjADORst.EOF Then MsgBox "Your query (" & mstrSQL & ") returned no records! " _ & "The default query to return all records will now be rerun.", _ vbExclamation, _
"ADO Example" 'reload the form with all the records cmdAllData_Click Else MsgBox "Your query returned " & mobjADORst.RecordCount & " records.", _ vbInformation, _ "ADO Example" 'load data into the text boxes Call DataLoad End If Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description
End Sub
11. Save and run. Note: When entering the "Like" criteria for City and/or State, you can use the wildcard character % to represent any number of characters and the wildcard character _ (underscore) the represent a single character. For example, entering "M%" for the City criteria would return all rows where the city field begins with the letter "M". " M".
Download the project files for this sample application here here..
Sample Application 3
Sample Application 3 demonstrates how to add, update, and delete records with ADO.
When the application is first run, the user is prompted to enter a minimum asking price to possibly limit the number of records they want to work with (i.e., "I only want to work with properties that are selling for $200,000 or more). If the user wants to work with all properties, they would simply
accept the default of 0 from the prompt. If the user clicks the Cancel button, the application will end.
Once the user has entered the minimum asking price, the main screen of the application is displayed. Initially, the screen is in "browse" mode, where the user can use the navigation buttons to move to the first, previous, next or last record. The data cannot be edited in this mode. If they want to initiate an add or an update, delete de lete a record, or exit the application, they may do so via the appropriate button. Saving or cancelling is not applicable in this mode, so those buttons are disabled.
If the user clicks the Add button, the fields on the screen are enabled and cleared, and the user can enter the information for the new property. All buttons except Save and Cancel are now disabled. After the user has made entries in the fields, he or she would click Save to add the new record to the database table, or, if they changed their mind, would click Cancel to discard the new record. In either case (clicking Save or Cancel) the user is returned to browse mode. When Save is clicked, the application validates the entries and will only save the record if all fields pass edit (otherwise, a message will appear indicating the problem entry and focus will be set to the problem field).
If the user clicks the Update button, the fields on the screen are enabled and the user can modify any or all of the fields (except for the Property Number, which is the primary key of the table). All buttons except Save and Cancel are now disabled. After the user has made modifications in the desired fields, he or she would click Save to update the record to the database table, or, if they changed their mind, would click Cancel to discard the changes. In either case (clicking Save or Cancel) the user is returned to browse mode. When Save is clicked, the application validates the entries and will only save the record if all fields pass edit (otherwise, a message will appear indicating the problem entry and focus will be set to the problem field).
If the user clicks the Delete button, the user is asked to confirm that they want to delete the current record. If they respond Yes, the record is deleted from the database table, and the main screen shows the next record in the table.
To build Sample Application 3, start a new VB project and perform p erform the following steps.
•
From the Project -> References menu, check Microsoft ActiveX Data Objects 2. x Library x Library and click OK.
•
This project uses the StatusBar control, so include the Microsoft Windows Common Controls 6.0 (SP6) from the Components dialog box, accessed from the Project -> Components menu. Check this item and click OK.
•
Create the form shown below. The settings for the various controls are given below.
•
There are nine textboxes in the main frame of the form. The names and MaxLength settings for these are given below:
•
Name
Properties
txtPropNo txtEmpNo txtAddress txtCity txtState txtZip txtBeds txtBaths txtAsking
MaxLength: 5 MaxLength: 4 MaxLength: 20 MaxLength: 15 MaxLength: 2 MaxLength: 5 MaxLength: 1 MaxLength: 3 (allows fractional amount, like 1.5) MaxLength: 0 (not specified)
Set up the Command Buttons as follows:
Name
Caption
cmdMoveFirst cmdMovePrevious cmdMoveNext cmdMoveLast cmdAdd cmdUpdate cmdDelete
<< < > >> Add Update Delete
cmdSave cmdCancel cmdExit
•
Save Cancel Exit
All controls on your form should have their TabIndex property set such that the tabbing order is correct.
•
Add a Module to the project, name it modCommon , and enter the code shown below. The code contains procedures described as follows:
CenterForm ValidKey
Sub to center a form on the screen Function to validate a keystroke for use in the KeyPress event of a
ConvertUpper
textbox Function to convert an alphabetic character entered in a textbox to
SelectTextBoxText
uppercase, used in the KeyPress event of a textbox Sub to highlight the text of a textbox when it receives focus. Used in
TabToNextTextBox
the GotFocus event of a textbox. Sub to "autotab" from one textbox to another when maximum number of characters that can be entered into the first textbox has
UnFormatNumber
been reached. Function to strip out non-numeric characters (dollar signs, commas, etc.) from a formatted number.
Option Explicit
Public Const gstrNUMERIC_DIGITS As String = "0123456789" Public Const gstrUPPER_ALPHA_PLUS As String = "ABCDEFGHIJKLMNOPQRSTUVWXYZ,'-"
Public gblnPopulating As Boolean
'----------------------------------------------------------------------Public Sub CenterForm(pobjForm As Form)
'-----------------------------------------------------------------------
With pobjForm .Top = (Screen.Height - .Height) / 2 .Left = (Screen.Width - .Width) / 2 End With
End Sub
'----------------------------------------------------------------------Public Function ValidKey(pintKeyValue As Integer, _ pstrSearchString As String) As Integer '-----------------------------------------------------------------------
' Common function to filter out keyboard characters passed to this ' function from KeyPress events. ' ' Typical call: ' KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS) '
If pintKeyValue < 32 _ Or InStr(pstrSearchString, Chr$(pintKeyValue)) > 0 Then 'Do nothing - i.e., accept the control character or any key ' in the search string passed to this function ... Else 'cancel (do not accept) any other key ... pintKeyValue = 0
End If
ValidKey = pintKeyValue
End Function
'----------------------------------------------------------------------Public Function ConvertUpper(pintKeyValue As Integer) As Integer '-----------------------------------------------------------------------
' Common function to force alphabetic keyboard characters to uppercase ' when called from the KeyPress event.
' Typical call: ' KeyAscii = ConvertUpper(KeyAscii) '
If Chr$(pintKeyValue) >= "a" And Chr$(pintKeyValue) <= "z" Then pintKeyValue = pintKeyValue - 32 End If
ConvertUpper = pintKeyValue
End Function
'---------------------------------------------------------------------------Public Sub SelectTextBoxText(pobjTextbox As TextBox)
'----------------------------------------------------------------------------
With pobjTextbox .SelStart = 0 .SelLength = Len(.Text) End With
End Sub
'---------------------------------------------------------------------------Public Sub TabToNextTextBox(pobjTextBox1 As TextBox, pobjTextBox2 As TextBox) '----------------------------------------------------------------------------
If gblnPopulating Then Exit Sub If pobjTextBox2.Enabled = False Then Exit Sub If Len(pobjTextBox1.Text) = pobjTextBox1.MaxLength Then pobjTextBox2.SetFocus End If
End Sub
'---------------------------------------------------------------------------Public Function UnFormatNumber(pstrNumberIn As String) As String '----------------------------------------------------------------------------
Dim lngX As Long Dim strCurrChar As String Dim strNumberOut As String strNumberOut = "" For lngX = 1 To Len(pstrNumberIn) strCurrChar = Mid$(pstrNumberIn, lngX, 1) If InStr("0123456789.", strCurrChar) > 0 Then strNumberOut = strNumberOut & strCurrChar End If Next UnFormatNumber = strNumberOut
End Function
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Code the General Declarations section as shown below. Here, as in the previous sample application, two ADO object variables, mobjADOConn and mobjADORst , are defined at the form level, as are some other form-level variables that will be needed.
Option Explicit
Dim mobjADOConn As ADODB.Connection Dim mobjADORst As ADODB.Recordset Private mstrSQL As String Private mdblMinAsking As Double Private mblnUpdatePending As Boolean Private mstrUpdateType As String
Private mavntUSStates As Variant
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Code the Form_Load event as shown below. In it, a programmer-defined Sub named GetMinimumAsking is called (that routine is the one that displays the initial prompt to the
user to enter the minimum asking price of the properties they want to work with). Then, the variant array mavntUSStates is loaded with the 50 US state abbreviations, needed for validating the state input by the user. This is followed by a call to the CenterForm sub. Then, the ADO connection object (mobjADOConn) is instantiated, its ConnectionString property is set, and the Open method is invoked so that we can use the Property database in the application. This is followed by a call to the programmer-defined Sub GetPropertyData (which runs the query to create the recordset that will be used to browse the Property table records), followed by a call to the programmer-defined Sub SetFormState (which enables and disables controls at the appropriate time).
'---------------------------------------------------------------------------Private Sub Form_Load() '---------------------------------------------------------------------------On Error GoTo LocalError ' obtain the minimum asking price for the properties to be worked with GetMinimumAsking ' load the array of states to be used for validation mavntUSStates = Array("AK", "AL", "AR", "AZ", "CA", "CO", "CT", "DC", _ "DE", "FL", "GA", "HI", "IA", "ID", "IL", "IN", _ "KS", "KY", "LA", "MA", "MD", "ME", "MI", "MN", _ "MO", "MS", "MT", "NC", "ND", "NE", "NH", "NJ", _ "NM", "NV", "NY", "OH", "OK", "OR", "PA", "RI", _ "SC", "SD", "TN", "TX", "UT", "VA", "VT", "WA", _ "WI", "WV", "WY") 'center the form: CenterForm Me ' Connect to the Property database: Set mobjADOConn = New ADODB.Connection mobjADOConn.ConnectionString = "DSN=PropDB;Uid=admin;Pwd=;"
mobjADOConn.Open
Call GetPropertyData
SetFormState False
Exit Sub
LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
Code the GetMinimumAsking Sub, which uses the InputBox function to prompt to the user to enter the minimum asking price of the properties they want to work with. The resulting value is then stored in the form-level variable mdblMinAsking .
'---------------------------------------------------------------------------Private Sub GetMinimumAsking() '---------------------------------------------------------------------------Dim strInputBoxPrompt As String Dim strAsking As String
strInputBoxPrompt = "Enter the minimum asking price (for example, 200000) " _ & "for the properties that you want to work with this session." _ & vbNewLine _ & "To work with ALL properties, leave the default of zero." strAsking = InputBox(strInputBoxPrompt, "Minimum Asking Price", "0") If strAsking = "" Then
' user clicked Cancel button on the input box, so end the app End End If mdblMinAsking = Val(strAsking)
End Sub
Code the GetPropertyData Sub, which builds the SQL to get the property records meeting the minimum asking price condition. The Recordset object is then instantiated, its CursorLocation property is set, and its Open method is invoked to execute the SQL and return the resultset. This is done in a loop in case the resultset does not return any records due to the fact no records in the table met the asking price condition. In that situation, the user is given the oppo rtunity to specify a different asking price value. Following this, the programmer-defined Sub PopulateFormFields is called (which displays the fields from the current record in their
corresponding textboxes on the form).
'---------------------------------------------------------------------------Private Sub GetPropertyData() '----------------------------------------------------------------------------
On Error GoTo LocalError Dim blnGotData As Boolean blnGotData = False Do 'select or reload the data to be displayed: mstrSQL = "select propno" _ & " , empno" _ & " , address" _ & " , city" _
& " , state" _ & " , zip" _ & " , beds" _ & " , baths" _ & " , asking" _ & " from property" _ & " where asking >= " & mdblMinAsking _ & " order by propno" Set mobjADORst = New ADODB.Recordset mobjADORst.CursorLocation = adUseClient mobjADORst.Open mstrSQL, mobjADOConn, adOpenDynamic, adLockOptimistic, adCmdText If mobjADORst.EOF Then If MsgBox("There are no properties with an asking price >= " _ & Format$(mdblMinAsking, "Currency") _ & ". Do you want to try again with a different value?", _ vbYesNo + vbQuestion, _ "Asking Price") _ = vbYes Then GetMinimumAsking Else End End If Else blnGotData = True End If Loop Until blnGotData 'load data into the text boxes Call PopulateFormFields Exit Sub LocalError:
MsgBox Err.Number & " - " & Err.Description
End Sub
Code the PopulateFormFields Sub, which assigns the fields from the current record to their corresponding textboxes on the form. Note that the gblnPopulating Boolean variable is set to True prior to the assignments and set to False after the assignments. This value is used to control whether or not certain code executes in the event procedures for some of these textboxes. The Sub SetRecNum is then called.
'---------------------------------------------------------------------------Private Sub PopulateFormFields() '---------------------------------------------------------------------------On Error GoTo LocalError
gblnPopulating = True
'copy the data from the resultset to the text boxes: txtPropNo.Text = mobjADORst.Fields("propno") txtEmpNo.Text = mobjADORst.Fields("empno") txtAddress.Text = mobjADORst.Fields("address") txtCity.Text = mobjADORst.Fields("city") txtState.Text = mobjADORst.Fields("state") txtZip.Text = mobjADORst.Fields("zip") txtBeds.Text = mobjADORst.Fields("beds") txtBaths.Text = mobjADORst.Fields("baths") txtAsking.Text = Format$(mobjADORst.Fields("asking"), "Currency") gblnPopulating = False
Call SetRecNum Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description
End Sub
Code the SetRecNum Sub. This sub is identical to the one used in Sample Application 2. It displays the number of the current record at the bottom of the screen using the AbsolutePosition and RowCount properties of the Recordset object.
'---------------------------------------------------------------------------Private Sub SetRecNum() '---------------------------------------------------------------------------StatusBar1.SimpleText = "row " & mobjADORst.AbsolutePosition _ & " of " & mobjADORst.RecordCount End Sub
Code the SetFormState Sub, which takes in a Boolean argument used to set the Enabled property of the controls on the form. Based on whether the value True or False is passed to this sub, this sub ensures that the textboxes are enabled for adds and updates and disabled for browsing; it also ensures that the various command buttons are enabled or disabled at the appropriate time. This Sub also sets the form-level Boolean variable mblnUpdatePending .
'---------------------------------------------------------------------------Private Sub SetFormState(pblnEnabled As Boolean) '----------------------------------------------------------------------------
txtPropNo.Enabled = pblnEnabled txtEmpNo.Enabled = pblnEnabled txtAddress.Enabled = pblnEnabled txtCity.Enabled = pblnEnabled txtState.Enabled = pblnEnabled txtZip.Enabled = pblnEnabled txtBeds.Enabled = pblnEnabled txtBaths.Enabled = pblnEnabled txtAsking.Enabled = pblnEnabled
cmdSave.Enabled = pblnEnabled cmdCancel.Enabled = pblnEnabled cmdAdd.Enabled = Not pblnEnabled cmdUpdate.Enabled = Not pblnEnabled cmdDelete.Enabled = Not pblnEnabled cmdExit.Enabled = Not pblnEnabled cmdMoveFirst.Enabled = Not pblnEnabled cmdMoveNext.Enabled = Not pblnEnabled cmdMovePrevious.Enabled = Not pblnEnabled cmdMoveLast.Enabled = Not pblnEnabled mblnUpdatePending = pblnEnabled
End Sub
Code the Form_Unload event. In it, the form-level Boolean variable mblnUpdatePending is tested to see if (well, an update is pending – i.e., whether an add or update is in progress). If the user is in the middle of an add a dd or update and then clicks the "X" button on the upper-right corner of the form, they will receive the message that they must save or cancel prior to exiting the application, and the form will NOT be unloaded (because we are assigning a non-zero value to
the Cancel argument in that situation). Provided that an add or update is not in progress, we set the database objects to Nothing and the Unload will complete.
'---------------------------------------------------------------------------Private Sub Form_Unload(Cancel As Integer) '----------------------------------------------------------------------------
If mblnUpdatePending Then MsgBox "You must save or cancel the current operation prior to exiting.", _ vbExclamation, _ "Exit" Cancel = 1 Else Set mobjADORst = Nothing Set mobjADOConn = Nothing End If End Sub
Code the events for the various Textboxes as shown below. The code in these events ensure the following: •
For all, highlight the text in the textbox when it receives focus.
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For all but the last textbox, if the maximum number of characters typed into the textbox is reached, auto-tab to the next textbox.
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Only numeric digits should be entered into the property number, employee number, zip codes, and beds textboxes.
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Only numeric digits and optionally one decimal point should be entered into the baths and asking textboxes.
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Force uppercase on the state textbox.
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When the asking textbox receives focus, the value in there should be unformatted. When the asking textbox loses focus, its value should be formatted as currency.
'---------------------------------------------------------------------------' Textbox events '----------------------------------------------------------------------------
' property # Private Sub txtPropNo_GotFocus() SelectTextBoxText txtPropNo End Sub Private Sub txtPropNo_KeyPress(KeyAscii As Integer) KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS) End Sub Private Sub txtPropNo_Change() TabToNextTextBox txtPropNo, txtEmpNo End Sub
' emp # Private Sub txtEmpNo_GotFocus() SelectTextBoxText txtEmpNo End Sub Private Sub txtEmpNo_KeyPress(KeyAscii As Integer) KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS) End Sub Private Sub txtEmpNo_Change() TabToNextTextBox txtEmpNo, txtAddress End Sub
' address Private Sub txtAddress_GotFocus() SelectTextBoxText txtAddress End Sub Private Sub txtAddress_Change() TabToNextTextBox txtAddress, txtCity End Sub
' city Private Sub txtCity_GotFocus() SelectTextBoxText txtCity End Sub Private Sub txtCity_Change() TabToNextTextBox txtCity, txtState End Sub
' state Private Sub txtState_GotFocus() SelectTextBoxText txtState End Sub Private Sub txtState_KeyPress(KeyAscii As Integer) KeyAscii = ConvertUpper(KeyAscii) End Sub Private Sub txtState_Change() TabToNextTextBox txtState, txtZip End Sub
' zip Private Sub txtZip_GotFocus() SelectTextBoxText txtZip
End Sub Private Sub txtZip_KeyPress(KeyAscii As Integer) KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS) End Sub Private Sub txtZip_Change() TabToNextTextBox txtZip, txtBeds End Sub
' beds Private Sub txtBeds_GotFocus() SelectTextBoxText txtBeds End Sub Private Sub txtBeds_KeyPress(KeyAscii As Integer) KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS) End Sub Private Sub txtBeds_Change() TabToNextTextBox txtBeds, txtBaths End Sub
' baths Private Sub txtBaths_GotFocus() SelectTextBoxText txtBaths End Sub Private Sub txtBaths_KeyPress(KeyAscii As Integer) KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS & ".") ' if text already has a decimal point, do not allow another ... If Chr$(KeyAscii) = "." And InStr(txtBaths.Text, ".") > 0 Then KeyAscii = 0 End If End Sub
Private Sub txtBaths_Change() TabToNextTextBox txtBaths, txtAsking End Sub
' asking price Private Sub txtAsking_GotFocus() txtAsking.Text = UnFormatNumber(txtAsking.Text) SelectTextBoxText txtAsking End Sub Private Sub txtAsking_KeyPress(KeyAscii As Integer) KeyAscii = ValidKey(KeyAscii, gstrNUMERIC_DIGITS & ".") ' if text already has a decimal point, do not allow another ... If Chr$(KeyAscii) = "." And InStr(txtAsking.Text, ".") > 0 Then KeyAscii = 0 End If End Sub Private Sub txtAsking_LostFocus() txtAsking.Text = Format$(txtAsking.Text, "Currency") End Sub
Code the events for the navigation buttons as shown below, using the resultset "Move" methods to move to the first, last, next, or previous record, respectively. '---------------------------------------------------------------------------Private Sub cmdMoveFirst_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MoveFirst
Call PopulateFormFields Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
'---------------------------------------------------------------------------Private Sub cmdMoveLast_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MoveLast Call PopulateFormFields Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
'---------------------------------------------------------------------------Private Sub cmdMoveNext_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MoveNext If mobjADORst.EOF Then Beep mobjADORst.MoveLast
End If Call PopulateFormFields Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
'---------------------------------------------------------------------------Private Sub cmdMovePrevious_Click() '---------------------------------------------------------------------------On Error GoTo LocalError
mobjADORst.MovePrevious If mobjADORst.BOF Then Beep mobjADORst.MoveFirst End If Call PopulateFormFields Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
Code the Click event for the cmdAdd button. In it, the textboxes are cleared, the SetFormState sub is called (passing it a parameter of True, which will enable the textboxes and the Save and Cancel buttons and disable all the other buttons), set the form-level variable mstrUpdateType to "A" (indicating that an add is pending) and sets focus to the Property Number field. '----------------------------------------------------------------------------
Private Sub cmdAdd_Click() '----------------------------------------------------------------------------
On Error GoTo LocalError
'clear all the text boxes: txtPropNo.Text = "" txtEmpNo.Text = "" txtAddress.Text = "" txtCity.Text = "" txtState.Text = "" txtZip.Text = "" txtBeds.Text = "" txtBaths.Text = "" txtAsking.Text = "" SetFormState True mstrUpdateType = "A" txtPropNo.SetFocus Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
Code the Click event for the cmdUpdate button. In it, the SetFormState sub is called (passing it a parameter of True, which will enable the textboxes and the Save and Cancel buttons and disable all the other buttons), set the form-level variable mstrUpdateType to "U" (indicating that an update is pending), disables the Property Number field (because it is the primary key and should not be changed) and sets focus to the Employee Number field.
'---------------------------------------------------------------------------Private Sub cmdUpdate_Click() '----------------------------------------------------------------------------
On Error GoTo LocalError
SetFormState True mstrUpdateType = "U" ' being that propno is the primary key, it should not be updatable txtPropNo.Enabled = False txtEmpNo.SetFocus Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
Code the Click event for the cmdSave button. The user would click this button after they have completed entries for an add or update. This sub first invokes the ValidateAllFields function, which returns a Boolean indicating whether or not all entries passed their edit checks. If not, we exit the sub and the record is not saved; the user remains in "update pending" mode and has the opportunity to correct the entries. Provided that validation is successful, the sub proceeds. The mstrUpdateType variable is checked to see whether we are dealing with an add or an update.
If we are dealing with an add, we invoke the AddNew method of the Recordset object. The AddNew method prepares a new row you can edit and subsequently add to the Recordset object
using the Update method. After you modify the new row, you must use the Update method to save the changes and add the row to the result set. No changes are made to the database until you use the Update method. (The Update method is invoked after the content of the textboxes has been assigned to the database fields.)
If we are dealing with an update, we can just start modifying the fields (provided an appropriate cursor type has been selected) – unlike DAO and RDO, ADO does not use an Edit method. Changes made to the current row’s columns are copied to the copy buffer. After you make the desired changes to the row, use the Update method to save your changes or the CancelUpdate method to discard them. (If you move on to a nother record without invoking Update, your changes will be lost.) The content of the textboxes is assigned to the database fields, then the Update method is invoked. The Update method saves the contents of the copy buffer row to a specified updatable Recordset object and discards the copy buffer. The mstrUpdateType variable is checked once again, and if we are dealing with an add, there is some extra work to do. Although the new record has been added, the original resultset still does not contain the new record. The Requery method must be invoked, which updates the data in a Recordset object by re-executing the query on which the object is based. The Find method is then used to position to the new record. The ADO Find method has the following syntax:
RecordsetObject .Find .Find Criteria, SkipRows, SearchDirection, Start
The Criteria argument is a String value that specifies the column name, comparison operator, and value to use in the search. Only a single-column name may be specified in criteria; multicolumn searches are not supported. The comparison operator may be ">" (greater than), "<" (less than), "=" (equal), ">=" (greater than or equal), "<=" (less than or equal), "<>" (not equal), or "like" (pattern matching). The value may be a string, floating-point number, or date. String values are delimited with single quotes or "#" (number sign) marks (for example, "state = 'WA'" or "state = #WA#"). Date values are delimited with "#" (number sign) marks (for example, "start_date > #7/22/97#"). These values can contain hours, minutes, and seconds to indicate time stamps, but should not contain milliseconds or errors will occur. If the comparison operator is "like", the string value may contain an asterisk (*) to find one or more occurrences of any character or substring. For example, "state like 'M*'" matches Maine and Massachusetts. You can also use leading and trailing asterisks to find a substring contained within the values. For example, "state like '*as*'" matches Alaska, Arkansas, and Massachusetts. Asterisks Asterisks can be used only at the end of a criteria string, or together at both the beginning and end of a criteria string, as shown
above. You cannot use the asterisk as a leading wildcard ('*str'), or embedded wildcard ('s*r'). This will cause an error. e rror. SkipRows is an optional Long value, whose default is zero, that specifies the row offset from the
current row (or bookmark row specified by the Start argument, if present) to begin the search. By default, the search will start on the current row. SearchDirection is an optional value that determines in which direction the search is performed.
The value is specified by the constants adSearchForward (the default) or adSearchBackward, which equate to values of 1 or -1, respectively.
Start is an optional Variant bookmark that functions as the starting position for the search.
Note: Unlike DAO, ADO does not have a "NoMatch" property. If the ADO Find method is unsuccessful, the record pointer is positioned at the end of the Recordset. The SetRecNum sub is then be called to display the status bar information about the new record. The SetFormState sub is then called with a parameter of False, which causes the textboxes and the Save and Cancel buttons to be disabled and all other buttons to be enabled. Note that in the statement that assigns the contents of the txtAsking textbox to the asking field of the table, our UnFormatNumber function is used to strip off the non-numeric characters. This is because we are using a display format that includes a dollar sign and commas on the txtAsking control, and an error would occur if we attempted to assign this directly to the asking field, which is defined as numeric. '---------------------------------------------------------------------------Private Sub cmdSave_Click() '----------------------------------------------------------------------------
On Error GoTo LocalError
If Not ValidateAllFields Then Exit Sub
If mstrUpdateType = "A" Then mobjADORst.AddNew Else ' We can just update the fields. No explicit Edit method ' is available or needed. End If 'save the data to the database: mobjADORst.Fields("propno") = txtPropNo.Text mobjADORst.Fields("empno") = txtEmpNo.Text mobjADORst.Fields("address") = txtAddress.Text mobjADORst.Fields("city") = txtCity.Text mobjADORst.Fields("state") = txtState.Text mobjADORst.Fields("zip") = txtZip.Text mobjADORst.Fields("beds") = txtBeds.Text mobjADORst.Fields("baths") = txtBaths.Text mobjADORst.Fields("asking") = UnFormatNumber(txtAsking.Text) mobjADORst.Update
If mstrUpdateType = "A" Then 'after the new record is added, the db must be re-queried 'so that the resultset contains the new record: mobjADORst.Requery ' reposition to the record just added mobjADORst.Find "propno = " & txtPropNo.Text 'display status info about the new record SetRecNum End If Reset:
SetFormState False Exit Sub LocalError: MsgBox Err.Number & " - " & Err.Description Resume Reset End Sub
Code the Click event for the cmdDelete button. The user is first asked to confirm that they want to delete the record, and if so, the Delete method of the resultset object is invoked, which deletes the current row in an updatable resultset object. The Requery method is then invoked so that the record is removed from the resultset that the user is working with. The Find method is then invoked to position the next record after the deleted one. If it was the last record that was deleted, then we position to the "new" last record using the MoveLast property. PopulateFormFields must then be called to display the contents of the new current record.
'---------------------------------------------------------------------------Private Sub cmdDelete_Click() '----------------------------------------------------------------------------
On Error GoTo LocalError 'when the current record is deleted, the current location in the recordset 'is invalid. use the Requery method to re-execute the query and update 'the data. If MsgBox("Are you sure you want to delete this record?", _ vbYesNo + vbQuestion, _ "Delete") = vbNo Then Exit Sub End If
mobjADORst.Delete mobjADORst.Requery ' reposition to one past the record just deleted mobjADORst.Find "propno > " & txtPropNo.Text ' If it was the last record that was deleted, the Find method will ' come back with EOF, in which case we should MoveLast to position ' us to the "new" last record ... If mobjADORst.EOF Then mobjADORst.MoveLast 'load data into the text boxes: Call PopulateFormFields
Exit Sub
LocalError: MsgBox Err.Number & " - " & Err.Description End Sub
The ValidateAllFields function, which returns a Boolean value indicating whether or not all fields have passed validation checks. This function calls upon two "helper" functions: PropertyExists and ValidState . When the user is doing an add, the PropertyExist function is called to see whether or not the proposed Property Number is already being used in the Property table. If so, the user is informed that they can't use that nu mber (because it is the primary key and must be unique) and so they must use a different number. The ValidState ValidState routine is called to ensure that the user has entered a valid US state. The code for all three functions is shown below.
'---------------------------------------------------------------------------Private Function ValidateAllFields() As Boolean '----------------------------------------------------------------------------
ValidateAllFields = False 'guilty until proven innocent If mstrUpdateType = "A" Then If txtPropNo.Text = "" Then MsgBox "Property # must not be blank.", vbExclamation, "Property #" txtPropNo.SetFocus Exit Function ElseIf PropertyExists Then MsgBox "Property # already exists. Please use a different #.", _ vbExclamation, _ "Property #" txtPropNo.SetFocus Exit Function End If End If If txtEmpNo.Text = "" Then MsgBox "Emp # must not be blank.", vbExclamation, "Emp #" txtEmpNo.SetFocus Exit Function End If If txtAddress.Text = "" Then MsgBox "Address must not be blank.", vbExclamation, "Address" txtAddress.SetFocus Exit Function End If If txtCity.Text = "" Then MsgBox "City must not be blank.", vbExclamation, "City" txtCity.SetFocus Exit Function End If If Not ValidState Then
MsgBox "Missing or invalid state.", vbExclamation, "State" txtState.SetFocus Exit Function End If If txtZip.Text = "" Or Len(txtZip.Text) = 5 Then ' it's OK Else MsgBox "Zip code must either be blank or exactly 5 digits.", _ vbExclamation, _ "Zip Code" txtZip.SetFocus Exit Function End If If Val(txtBeds.Text) = 0 Then MsgBox "Beds must not be zero.", vbExclamation, "Beds" txtBeds.SetFocus Exit Function End If If Val(txtBaths.Text) = 0 Then MsgBox "Baths must not be zero.", vbExclamation, "Baths" txtBaths.SetFocus Exit Function End If If Val(UnFormatNumber(txtAsking.Text)) = 0 Then MsgBox "Asking must not be zero.", vbExclamation, "Asking" txtAsking.SetFocus Exit Function End If ' if we make it here, all fields have passed edit ValidateAllFields = True
End Function
'------------------------------------------------------------------------------Private Function ValidState() As Boolean '-------------------------------------------------------------------------------
Dim lngX As Long Dim blnStateFound As Boolean blnStateFound = False For lngX = 0 To UBound(mavntUSStates) If txtState.Text = mavntUSStates(lngX) Then blnStateFound = True Exit For End If Next ValidState = blnStateFound End Function
'---------------------------------------------------------------------------Private Function PropertyExists() As Boolean '----------------------------------------------------------------------------
Dim objTempRst As New ADODB.Recordset Dim strSQL As String
strSQL = "select count(*) as the_count from property where propno = " & txtPropNo.Text
objTempRst.Open strSQL, mobjADOConn, adOpenForwardOnly, , adCmdText If objTempRst("the_count") > 0 Then PropertyExists = True Else PropertyExists = False End If
End Function
Code the Click event for the cmdCancel button. The user would click this button if, during an add or update, they decide to abandon the operation. Here, PopulateFormFields is called to reset the textboxes to their content prior to the user clicking the Add or Update button, and SetFormState is called with a parameter of False, which causes the textboxes and the Save and
Cancel buttons to be disabled and all other buttons to be enabled. '---------------------------------------------------------------------------Private Sub cmdCancel_Click() '----------------------------------------------------------------------------
PopulateFormFields SetFormState False End Sub
Code the Click event for the cmdExit button, which issues the Unload Me statement to fire the Form_Unload event, which will unload the form and a nd end the application.
'---------------------------------------------------------------------------Private Sub cmdExit_Click()
'----------------------------------------------------------------------------
Unload Me End Sub
Download the project files for this sample application here here..
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Comments Thu, 01/21/2010 - 08:50 — Abo Omar (not verified)
Thanks alot Hi Thanks alot for fantastic job If possible, please write about DataReport in visual basic Good Bye
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Tue, 01/19/2010 - 03:15 — Nikunj (not verified)
Help
i m using Visual Basib 6.0 and and MS-Access database..my database is on Web Server and want to connect tht database from VB...how can i......?
plz Help me...
Thanks & Regards, Nikunj
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Thu, 11/26/2009 - 04:17 — Dins (not verified )
Very Good Tutorialssss ..... a very good tutorial and I am proud as you can provide much inspiration for beginners and very helpful. I'm from Indonesia pleased with you and your tutorial helped me a lot. thank you very much. I am a beginner and could I learn from here to learn more.
Thanks Didin
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Sat, 10/31/2009 - 10:50 — Govind dx (not verified)
Great Thank you very much....
great......
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Fri, 10/09/2009 - 18:16 — NANDAKUMAR PK ( not verified)
I really congratulate you I really congratulate you for writing such a helpful tutorial .
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Sat, 10/03/2009 - 02:28 — Anonymous (not verified)
help i always get an error 445 object doesnt support this action which points to the recodset.update
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Fri, 10/02/2009 - 18:19 — Anonymous (not verifie d)
thank you i understand now thank you i understand now how ado works.. thank so much for sharing your knowlegde your tutorial is oso great and its easy to understands.. :D
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Tue, 08/04/2009 - 02:24 — Anonymous (not verified)
ADO tutorial Iam so glad i found the right website for the VB6 tutorial it really help me a lot. Thanks a lot.
Question: When am going to enable the Reference :Microsoft ActiveX Data Object 2.7 library i have found error: Name conflicts with existing module , project or object library.
Please help me what im going to do?
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Mon, 08/03/2009 - 20:47 — Novice_Filipino_Programmer (not verified)
... Great Tutorial , It helped me a lot thank you very much....
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Sun, 08/02/2009 - 01:07 — flash17 (not verified)
HELP!!!
can you please help me in my project.. i find it hard to fetch data from my database to populate the fields of my listview box... please send me some codes..
..by the way that was a great tutorial...very informative.. informative..
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Wed, 07/29/2009 - 05:07 — Mohit Kumar (not verified)
Kudos hey thats a great tutorial... great work man..... keep up the good work..
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Tue, 07/07/2009 - 20:03 — Vinod Merchant (not verified)
Superb Cudos! I regret not having seen this before today. I wonder if you have similar articles for C# or May be for VS 2005 etc Congratulations
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Fri, 06/19/2009 - 00:45 — ang sarap ng filling mo (not verified)
please send me this file plz please send me this file plz so i can debug it on may project
here's my email
[email protected]
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Fri, 06/19/2009 - 00:44 — ang sarap ng filling mo (not verified)
please send me this file plz please send me this file plz so i can debug it on may project
here's my email
[email protected]
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Sun, 05/10/2009 - 15:42 — Saeed_VB6 (not verified)
GREAT! Hi
gReAt WeBsItE & GrEaT tUtOrIaL
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VB6 Is Still ALIVE
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VB6 Is Still Poweful
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VB6 Has Still Great Performance
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VB6 Is anything you want...
i'm thankful.
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Sun, 05/10/2009 - 02:51 — Piyush Vishvas (not verified)
Thanks for easy vb6 training tutorials I heartily say thanks to you for such a great tutorial on ADO and Databases. It extremely helped me because you explained it with 3 different examples, which were still all parallel with each other. When I read them fully and practiced with it, then it was easy to understand the theory behind these codes. I am so happy that I found your website for learning vb6 and want to say thank you once again.
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Wed, 04/29/2009 - 07:25 — shekar (not verified)
wow..really great article wow..really great article which explains everything about ADO.Thanks a lot buddy.keep up your good work...
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Mon, 04/27/2009 - 06:01 — Anonymous (not verified)
Database? can anybody please tel me where can i find second database?That database?That is propery Databa Database..I se..I am not able to find that database.
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Wed, 04/22/2009 - 21:54 — Anonymous (not verified)
VB6 Hi, Why visual basic can't recognized the access 2000 file format? Help me pls.. ThankYou!!
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Mon, 04/20/2009 - 12:44 — Paddy (not verified)
Very useful tutorial This is a great tutorial!It helped me to finally understand ADO with databases.Thank you very much.
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Tue, 04/14/2009 - 21:03 — Uday
Thats called Thats called computerization, have nice and healthy life.
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Tue, 04/14/2009 - 19:56 — Anonymous (not verified)
need help pls. help me to make a program about library inventory system, wherein the librarian can identify which books are borrowed and which are available, thanks!!
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Tue, 04/07/2009 - 02:47 — AQrvin (not verified)
error Put the following code in the cmdNameOrder_Click event: adoBiblio.SQL = "select * from authors order by author" adoBiblio.Refresh
Put the following code in the cmdYearOrder_Click event: adoBiblio.SQL = "select * from authors order by [year born]" adoBiblio.Refresh
Put the following code in the cmdIDOrder_Click event: adoBiblio.SQL = "select * from authors order by au_id" adoBiblio.Refresh
· Save and run the program and see what happens when you click the buttons.
U will get method or data member not found. remove the .SQL and replace by .RecordSource
I dnt knw if there are more errors..
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Sat, 03/14/2009 - 10:07 — Pankaj Kumar Sharma (not verified)
best tutorials i think this is the best tutorial for vb+database on the internet
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Wed, 02/18/2009 - 04:37 — Ishan Mathur (not verified)
Great Tutorial Great Tutorial cum article Very helpful mostly to students
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Wed, 02/18/2009 - 01:43 — 03ProgRammeR03 (not verified)
help me please! How am i going to update a single field in just a single click ? Ex. Book (field name on the database)
'''''''''''''''''''''''''' '''''''''''''''''''''''''' Book ' '''''''''''''''''''''''''' '''''''''''''''''''''''''''
''''''''''''''''''''''''''' Science '''''''''''''''''''''''''' Mathematics '''''''''''''''''''''''''' English '''''''''''''''''''''''''''
how can i update all of the content of book(field name) in just a single click? What I'm trying to say is to make all of the contents of the book = "" just a single click... just like this:
'''''''''''''''''''''''''' '''''''''''''''''''''''''' Book ' '''''''''''''''''''''''''' ''''''''''''''''''''''''''' (no text) '''''''''''''''''''''''''' (no text) '''''''''''''''''''''''''' (no text) ''''''''''''''''''''''''''' please help me..
thankz...
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Sun, 02/15/2009 - 04:10 — Ajay (not verified)
Very Nice Very excellent tutorial ,it helps me lot!
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Sat, 01/17/2009 - 09:22 — Shrinivas (not verified)
Thanks a lot!! Excellent Work!! It helped me finally understand how ADODB actually works. this is a website i'd recommend top all my friends!!! Thanks a lot again!!!!
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Fri, 11/28/2008 - 20:53 — Anonymous (not verified)
hi pls. send to me this..... i need your help...
Pls. enumerate the procedures in wc a VB program can access a DB using data control... using code and in the properties window...
What are the advanta advantages ges and disadvantages of accessing a DB in code? in properties windows..
pls. reply back
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Wed, 11/12/2008 - 02:42 — babyqoh (not verified)
whatta article whatta article
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Tue, 10/28/2008 - 05:24 — KIM (not verified)
plzzzz waw your tutorial so excellent,,but can u help me i n my program? how to search a record?..plzzz tnx
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Tue, 10/21/2008 - 01:25 — habd (not verified)
ifihfit is fine keep it up ifihfit is fine keep it up OkKKKKKKKKKKKKKK!!!!!!!!!!!! OkKKKKKKKKKKKKKK!!!!!!!!!!!!!!
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Thu, 10/16/2008 - 02:14 — YTa (not verified)
Nice and sweet dcsHay folks this is owsm!!!!! Keep focus and help us to make world better. Thanks!
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Sat, 10/11/2008 - 07:56 — Andy Marshall (not verified)
DataSourceName & SQL property fields missing. This seems like a great tutorial but I'm having problems. I add the ADO Data Control but the 'DataSourceName' 'DataSourceName' and 'SQL' fields do not appear in the property tab.
If I right-click on the control and select 'ADODC Properties' I can change the field 'Use ODBC Data Source Name' to 'Biblio' and on the 'RecordSource' tab I can change the Command Text (SQL) to read 'select * from authors'.
When changing the properties at run-time I need to use different code :
Private Sub cmdIDOrde cmdIDOrder_Click() r_Click() adoBiblio.RecordSource adoBiblio.RecordS ource = "select * from authors order by au_id" adoBiblio.Refresh End Sub
The program runs as expected but I'm concerned about having to use different code. Does anybody have any ideas?
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Wed, 10/08/2008 - 05:40 — Anonymous (not verified)
Thanks a lot! Hi! Thank you so much for the tips and sample programs and codes in programming. It was really of great help to me. I hope I will be able to share some of my programs soon. :)
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Sun, 10/05/2008 - 01:24 — Deep (not verified)
can any body help me fdf Hi, I am new to VB6 i did some programing in c++ and java. I am struglling to make common module from which i can use connection and recordset so that i dont have to make seperate connection and recorset for each form. we can do that in c++ by making class. In vb6 i am confused. i was able to make sub in connecting sub in module but i not
able to pass connection object to different forms to create different recordsets. thanks thanks I
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Fri, 10/03/2008 - 23:19 — Akabane (not verified)
how to connect ado with the how to connect ado with the use of codes or coding.
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Thu, 09/17/2009 - 03:59 — joek (not ve rified)
re:how to connect with ado hi, first you have to activate the ado connection by going to project>references>microsoft project>references >microsoft activex data objects 6.0 then to components and select the ADO library next:
declare the connection object the you declare the recordset . e.g. dim conn as new ADODB.Connection dim rs as new ADODB.Connection dim strSQL as string next in form_load() event fill in the following code conn.open "fill in the source" strSQL="SELECT * FROM table_name"
rs.open strSQL,conn,adUseClient,AdLockOpt strSQL,conn,adUseClient,AdLockOptimistic imistic 'if using access the you are through with opening.
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Tue, 09/23/2008 - 02:12 — Anonymous (not verified)
Computerized registration im a new bie in programming...can anyone anyone help me to do a computerized registration in different type of organizaton using microsoft access in VB6...pls, thanks and god bless.....
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Mon, 09/22/2008 - 11:21 — Anonymous (not verified)
Hi Excellent Article.... Keep it up
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Fri, 09/19/2008 - 02:21 — Grubby (not verified)
Marvelous Thank you very much. This tutorial DOES HELP me a lot to understand ADO with Visual Basic. I manage to learn a lot fundament fundamental al but essential and neccessary knowledge about VB. thank you. bless you~
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Mon, 08/25/2008 - 11:01 — christian (not verified)
Great Article Thank You very much. I was looking for a tutorial to learn the basics of ADO and your step by step examples are excellent.
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Fri, 08/22/2008 - 02:50 — nad (not verified)
help
I'm trying to update something and a run time error occurs, its
runtime error 40002: 01000:[Microsoft][ODBC SQL Server Driver]Command has been aborted
can anyone help me with this???
nad
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Mon, 07/21/2008 - 09:28 — Shyam (not verified)
good work keep it up... good work.....
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Fri, 07/18/2008 - 21:47 — Tongan Crusader (not verified)
What a marvelous helper You are the one...if anyone is come to give u thanks he is a celever man Remember the story of leprosy in the bible..only one man return and gave thanks to Jesus...thanks Jesus...thanks to those who gave thanks to u...I am thinking of writing a site like this but use it in my language...I am so happy with you...I know youre blessed with all these good works....
Continue on this good work
The Tongan Crusader
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Fri, 07/04/2008 - 23:02 — russel_philippines (not verified)
wow!!! it helps me a lot to learn ADO database method.. Thanks!
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Tue, 07/01/2008 - 06:17 — Jamie Bates (not verified)
You are an asset **You are an asset to the development community. Please, keep up the great work. You have just motivated me to start building my sites.
Jamie
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Fri, 06/27/2008 - 06:23 — Anonymous (not verifie d)
This is a great example of This is a great example of SQL injection.
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Wed, 05/21/2008 - 13:27 — Anonymous (not verified)
Good work This is how a tutorial should be. Especially the fact that there are three tutorials in progressive complexity with about the right increase of complexity from one to the other.
Thank you Mo
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Mon, 04/14/2008 - 22:16 — Anonymous
nice!!!can u add more???with connection in Crystal Report please add an article with a crystal report connection.... connection....
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Thu, 02/14/2008 - 01:59 — Anonymous
Cursortypes, locktype, cursorlocation......... I'm a free lance system developer (programmer) mainly create my program through VB6, with a little add-ons on different support programs, ei Crystal report etc. I like the review
on the locktypes, l ocktypes, cursortypes, cursortypes, and cursorlocations, coz i kinda takeforgranted those basic option (like the locktype and cursortype, my combination are always, adopendynamic and adlockoptimistic ) till now im still using such combination, because because when i use different attribute, some of my program malfunction, specially when using the network or via web. I guess im used to it, and don't give a thing on other options. still it would be a good help it will improve, specially if i where to used so much memory, object or allocation. Care for any tips on combination on locktypes and cursortypes? And most of all, th CURSORLOCATION....... CURSORLOCATION....... what is the difference between the 2, aduseclient and aduseserve aduseserver? r? i know they have, but im a little of on finding it. can you enumerate all or atleast some major factor that give different affect on different cursorlocation. thanx
and another:I started on DAO and switch to ADO. may i ask, which is better, DAO or ADO?
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Mon, 01/28/2008 - 02:49 — Anonymous
Database Access With ADO Tutorial Very rich resource. More, please.
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Wed, 12/19/2007 - 03:31 — Anonymous
not accepting const dear all i tried the sample-3 , given under the tutorial ado samples, as soon as i enter the initial declaration "public const mstrnumeric_digits as string ="0123456789" "
it gives me an error
can anyone explain me how to solve it
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Wed, 11/28/2007 - 06:32 — Anonymous
Database Access with ADO I want to compliment you in writing such a great tutorial article on using ADO and Databases.. It was extremely helpful because you displayed 3 different examples, which Databases were still all parallel with each other. The more that I read through each of the examples and practiced with it, the clearer I started to understand the theory behind these codes. I am so glad that I came across your weblink and want to thank you once again.
Respectfully, Sam Maldonado
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