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In Access 2000 and later, an AutoNumber field may begin assigning extreme values, negatives, and even duplicates. The attempt to assign a duplicate fails if the field is primary key, so it may not be possible to save new records in an affected table.
Several issues can trigger this problem:
|An old bug||Apply JET 4 Service Pack (7 or later) to prevent the problem recurring. Use the code below to fix your AutoNumbers.|
|Appending data to a linked table.||Microsoft's workaround is discussed in knowledge base article 884185. Note that this issue is more generic than the kb article suggests: it occurs any time you specify the value for the AutoNumber when appending to a linked table, not just when appending from one linked table to another.|
|A badly-designed form, discussed below.||Redesign the form. Use the code below to fix the AutoNumber.|
|AutoNumber defined as Random or Replication ID.||Open your table in design view, select the AutoNumber field, and ensure Field Size is "Long Integer", and New Values is "Increment." (Not possible in replicated databases.)|
You may be able to solve the problem with a compact/repair. In Access 2007: Office Button | Manage. In earlier versions, Tools | Database Utilities.
Alternatively, the code below checks all tables in your database, and offers to fix any where the Seed of the AutoNumber is less than zero or below the existing values. The function returns the number of tables that were changed - zero if none had the problem. It does not alter the values of any duplicate values in the column.
The code does not work on attached tables: if your database is split, run it in the back end data file.
It works only with Access 2000 or later, but earlier versions do not have this problem.
Version 4 of JET supports altering the Seed for an AutoNumber (which is how they got it wrong.) The DAO library was not updated to handle the new feature, so we use ADOX.
The code performs these steps:
Function AutoNumFix() As Long 'Purpose: Find and optionally fix tables in current project where ' Autonumber is negative or below actual values. 'Return: Number of tables where seed was reset. 'Reply to dialog: Yes = change table. No = skip table. Cancel = quit searching. 'Note: Requires reference to Microsoft ADO Ext. library. Dim cat As New ADOX.Catalog 'Catalog of current project. Dim tbl As ADOX.Table 'Each table. Dim col As ADOX.Column 'Each field Dim varMaxID As Variant 'Highest existing field value. Dim lngOldSeed As Long 'Seed found. Dim lngNewSeed As Long 'Seed after change. Dim strTable As String 'Name of table. Dim strMsg As String 'MsgBox message. Dim lngAnswer As Long 'Response to MsgBox. Dim lngKt As Long 'Count of changes. Set cat.ActiveConnection = CurrentProject.Connection 'Loop through all tables. For Each tbl In cat.Tables lngAnswer = 0& If tbl.Type = "TABLE" Then 'Not views. strTable = tbl.Name 'Not system/temp tables. If Left(strTable, 4) <> "Msys" And Left(strTable, 1) <> "~" Then 'Find the AutoNumber column. For Each col In tbl.Columns If col.Properties("Autoincrement") Then If col.Type = adInteger Then 'Is seed negative or below existing values? lngOldSeed = col.Properties("Seed") varMaxID = DMax("[" & col.Name & "]", "[" & strTable & "]") If lngOldSeed < 0& Or lngOldSeed <= varMaxID Then 'Offer the next available value above 0. lngNewSeed = Nz(varMaxID, 0) + 1& If lngNewSeed < 1& Then lngNewSeed = 1& End If 'Get confirmation before changing this table. strMsg = "Table:" & vbTab & strTable & vbCrLf & _ "Field:" & vbTab & col.Name & vbCrLf & _ "Max: " & vbTab & varMaxID & vbCrLf & _ "Seed: " & vbTab & col.Properties("Seed") & _ vbCrLf & vbCrLf & "Reset seed to " & lngNewSeed & "?" lngAnswer = MsgBox(strMsg, vbYesNoCancel + vbQuestion, _ "Alter the AutoNumber for this table?") If lngAnswer = vbYes Then 'Set the value. col.Properties("Seed") = lngNewSeed lngKt = lngKt + 1& 'Write a trail in the Immediate Window. Debug.Print strTable, col.Name, lngOldSeed, " => " & lngNewSeed End If End If End If Exit For 'Table can have only one AutoNumber. End If Next 'Next column End If End If 'If the user chose Cancel, no more tables. If lngAnswer = vbCancel Then Exit For End If Next 'Next table. 'Clean up Set col = Nothing Set tbl = Nothing Set cat = Nothing AutoNumFix = lngKt End Function
There are other cases where Access can be fooled into setting the Seed of the AutoNumber incorrectly.
These steps will reproduce the problem in Access 2000, 2002, or 2003, with all service packs applied:
Subforms are designed to enter related records. The subform's foreign key field (named in LinkChildFields) therefore inherits the value of the main field's primary key (named in LinkMasterFields.) In the case above, this means that Access is trying to assign the existing primary key value from the first record to the new record being entered in the subform. Naturally that fails.
Unfortunately, the Seed of the AutoNumber also gets set to one more than the failed write. Since the Seed is below existing values, further attempt to add new records also fails, as Access tries to reassign existing values.
(Note that the Seed is reset only if the LinkChildFields contains the name of an object of type AccessField. The write still fails, but the Seed is not reset if LinkChildFields names an object of type Control, e.g. if there is a text box with that name in the subform.)
There is no valid reason for designing a main form and subform bound to the same table and linked on the AutoNumber field. Get rid of this bad design. Then use the code above to fix the problem with your AutoNumber so you can add new records to the table again.
There may also be other scenarios where JET is tricked into resetting the AutoNumber to an unusable value. If you believe you are found one, email email@example.com.
For code to examine a table and find out what the Seed of the AutoNumber is, see GetSeedAdox().
For code to reset the Seed for one table only, see: ResetSeed().
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This is a cached tutorial, reproduced with permission.
Have your say - comment on this article.
What did you think of 'Fixing AutoNumbers (AutoNumber bug in Jet 4.0)'?
|Dr. Shemy Carasso says...|
18 October 2009
Easy to understand and it worked perfectly...
Have your say...