Microsoft KB Archive/100465

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ACC1x: Preventing Users from Adding New Records

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Q100465

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The information in this article applies to:


 * Microsoft Access versions 1.0, 1.1

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SUMMARY
The DefaultEditing form property, when set to AllowEdits, allows users to both modify existing records and to add new records. Microsoft Access has no built-in mechanism to prevent users from adding new records.

MORE INFORMATION
The following example demonstrates a sample, user-defined Access Basic function that you can use to prevent users from entering new employees in the Employees form in the sample database NWIND.MDB:

  Type the following Access Basic function in a new or existing module:

     Function PreventNew Dim X        On Error Resume Next X = Screen.ActiveForm.Bookmark If Err = 3021 Then DoCmd GoToRecord, , A_LAST End Function

NOTE: There are two commas between GoToRecord and A_LAST above.   Change the OnCurrent property of the Employees form to read as follows:

     Form: Employees OnCurrent: =PreventNew

Note that the pointer is placed in the last record of the Employees form when you attempt to gain access to or navigate to the new record. 

How PreventNew Works
Whenever you navigate to a different record, the OnCurrent property runs the PreventNew function. This function attempts to reference the Bookmark property associated with the current record. All records are assigned a string, called a bookmark, that uniquely identifies each record.

However, a new record that has not yet been saved has no bookmark associated with it. Any attempt to reference the bookmark of a new record generates an error message. If an error occurs, the PreventNew function immediately performs a GoToRecord action to navigate to the last record in the form.

Using PreventNew with Forms That Contain No Records
If the table or query that the form is based on contains no records, PreventNew does not prevent you from adding a new record to the form. You must first test to see if records exist in the table or query prior to opening the form. You can use the following Access Basic function to test whether records exist in a table or query.

     Function RecordsExist (TableQueryName As String) Dim DB As Database Dim DS As Dynaset Set DB = CurrentDB On Error Resume Next Set DS = DB.CreateDynaset(TableQueryName) DS.MoveFirst If Err <> 0 Then RecordsExist = False Else RecordsExist = True End If    End Function

Given the name of the table or query, this function will return True (-1) if records exist, or False (0) if no records exist.

Another method you can use is the DCount function. However, the DCount function may be significantly slower than the RecordsExist function in that it must count all the records in the database whereas RecordsExist simply tests to see if there is a "first" record in the recordset.

Keywords : kbprg

Issue type : kbinfo

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