Adding field to MS Access Table using VBA

Question

I need to add a calculated field to an existing table. I am aware of two ways to do this and I'm wondering if anyone has any input on which is best and how to make them work:

1. Using TableDef.CreateField, then TableDef.Fields.Append
2. Using a DDL Alter Table ADD COLUMN statement

I tried using the first method, but I keep getting a 3211 error because Access could not lock the table. I don't have the table open. However, I am calling CreateField from a form that has accessed which fields currently exist in the table.

Here's the code for calling CreateField:

`
Public Sub AddFieldToTable(strTable As String, strField As String, nFieldType As     Integer)

    Dim db As DAO.Database
    Dim tdf As DAO.TableDef
    Dim fld As DAO.Field

    On Error GoTo ErrorHandler

    Set db = CurrentDb
    Set tdf = db.TableDefs(strTable)
    Set fld = tdf.CreateField(strField, nFieldType)
    tdf.Fields.Append fld

    MsgBox "The field named [" & strField & "] has been added to table [" & strTable & "]."

    Set tdf = Nothing
    Set db = Nothing

    Exit Sub

    ErrorHandler:
        MsgBox "An error has occurred. Number: " & Err.Number & ", description: " &        Err.Description
        Exit Sub

End Sub
`

I get the error on the tdf.fields.append line. Would executing an ALTER TABLE statement be better? What are the tradeoffs?

Answer 1

You can use DDL to create fields:

Long:

CurrentDb.Execute "ALTER TABLE t ADD COLUMN a Long not null", dbFailOnError 

(tack on NOT NULL IDENTITY(1,1) for an autonumber)

CurrentDb.Execute "ALTER TABLE t ADD COLUMN b text(100)", dbFailOnError 

Boolean:

CurrentDb.Execute "ALTER TABLE t ADD COLUMN c Bit not null", dbFailOnError 

DateTime:

CurrentDb.Execute "ALTER TABLE t ADD COLUMN d datetime null", dbFailOnError 

Memo:

CurrentDb.Execute "ALTER TABLE t ADD COLUMN e memo null", dbFailOnError 

Obviously, this lends itself well to functionalization, and you could just pass in your own eternal enum, combined with a Select, to construct the string and execute it:

Public Sub AddFieldToTable(TableName as string, FieldName as string, _
      FieldType as Long, FieldLen as Long, FieldAllowsNull as Boolean)

Dim FieldText as String

Select Case(FieldType)
    Case 0:
        FieldText = "Long"
    Case 1:
        FieldText = "text(" & FieldLen & ")"
    Case 2:
        FieldText = "bit"
    Case 3:
        FieldText = "datetime"
    Case 4:
        FieldText = "memo"

End Select

Dim Sql as string
Sql = "ALTER TABLE " & TableName & " ADD COLUMN " & FieldName & " " & FieldText

If FieldAllowsNull then
   Sql = Sql & " NULL"
Else
   Sql = Sql & " NOT NULL"
End If

CurrentDb.Execute Sql, dbFailOnError

End Sub