Recipe 6.6 Get a Complete List of Field Properties from a Table or Query

6.6.1 Problem

You want to get a list of fields in a table or query and their properties. The ListFields method is fine for certain situations, but it returns only a few of the fields' properties. Microsoft has also made it clear that this method will not exist in future releases of Access. How can you create a replacement for ListFields that supplies all the available field information?

6.6.2 Solution

In Access 1.x, the ListFields method was the only supported way to return a list of fields and their properties. Its usefulness is limited because it returns only a few field properties and always returns a snapshot. Using the more flexible Data Access Objects (DAO) hierarchy, however, you can get all the properties of field objects and create a replacement for the outdated ListFields method that returns all of a field's properties (or as many as you'd like), placing the results in a readily accessible table.

Open and run the frmListFields form from 06-06.MDB (see Figure 6-9). Choose Tables, Queries, or Both, and whether you wish to include system objects. Select an object from the Object combo box. After a moment, the form will display a list of fields and their properties in the Fields list box. Scroll left and right to see additional properties and up and down to see additional fields.

Figure 6-9. The frmListFields form

To use this technique in your applications, follow these steps:

Table 6-5. The acbListFields subroutine's parameters

Parameter	Example	Description
strName	"Customers"	The name of the table or query
blnTable	True	True if strName is a table, False if it is a query
strOutputTable	"tmpOutputFields"	The name of the table that will hold the list of field properties

Table 6-6. The acbListFields output table structure

Field name	Data type	Description
Name	String	The name of the field.
Type	Integer	The data type of the field as represented by an integer. Search Access help under ListFields to decode this value.
Size	Integer	The size of the field.
Attributes	Long Integer	The field's attributes. Search Access help under Attributes to decode this value.
SourceTable	String	The name of the field's underlying table. If the table is an attached table, this field will contain the name of the table as it exists in the source database.
SourceField	String	The name of the field.
CollatingOrder	Integer	The collating order of the table. Search Access help under CollatingOrder to decode this value.
AllowZeroLength	Integer	True if zero-length strings are allowed in the field; False otherwise.
DataUpdateable	Integer	True if the field is updateable; False otherwise.
DefaultValue	Text	The field's default value.
OrdinalPosition	Integer	The field's position in the table, starting at 0.
Required	Integer	True if the field requires an entry; False otherwise.
ValidationRule	String	The field's ValidationRule property.
ValidationText	String	The field's ValidationText property.
Caption	String	The field's Caption property.
ColumnHidden	Integer	True if the field is hidden in datasheet view; False otherwise.
ColumnOrder	Integer	The order in which the field appears in datasheet view.
ColumnWidth	Integer	The width of the field as it appears in datasheet view.
DecimalPlaces	Integer	The field's number of decimal places.
Description	Text	The field's description.
Format	Text	The field's format string.
InputMask	Text	The field's input mask string.

6.6.3 Discussion

The acbListFields subroutine uses a table-driven approach to populate the list fields output table with the properties of the fields in the input table or query. Here's the basic algorithm for acbListFields:

The acbListFields subroutine is shown here:

Public Sub acbListFields( _
 strName As String, blnTable As Boolean, _
 strOutputTable As String)
   ' Purpose:
   '     Saves a list of the most common field properties
   '     of a table or query to a table.
   
   Dim db As DAO.Database
   Dim rst As DAO.Recordset
   Dim tdf As DAO.TableDef
   Dim qdf As DAO.QueryDef
   Dim fld As DAO.Field
   Dim intFieldCount As Integer
   Dim intI As Integer
   Dim intJ As Integer
   Dim strOutputField As String
   
   On Error GoTo HandleErr
   
   Call acbMakeListTable(strOutputTable)

   Set db = CurrentDb( )
   Set rst = db.OpenRecordset(strOutputTable)

   ' If the input object is a table, use a TableDef.
   ' Otherwise, use a QueryDef.
   If blnTable Then
      Set tdf = db.TableDefs(strName)
      intFieldCount = tdf.Fields.Count
   Else
      Set qdf = db.QueryDefs(strName)
      intFieldCount = qdf.Fields.Count
   End If

    ' Iterate through the fields in the TableDef
    ' or QueryDef.
    For intI = 0 To intFieldCount - 1
       ' Create a new record for each field.
       rst.AddNew
       If blnTable Then
          Set fld = tdf.Fields(intI)
       Else
          Set fld = qdf.Fields(intI)
       End If
       ' Iterate through the fields in rst. The names of these fields
       ' are exactly the same as the names of the properties we wish
       ' to store in them, so we take advantage of this fact.
       For intJ = 0 To rst.Fields.Count - 1
          strOutputField = rst.Fields(intJ).Name
          rst.Fields(strOutputField) = _
           fld.Properties(strOutputField)
       Next intJ
       rst.Update
    Next intI
    
ExitHere:
   Set rst = Nothing
   Set qdf = Nothing
   Exit Sub

HandleErr:
   Select Case Err.Number
      Case 3270        ' Property not found.
         ' Skip the property if it can't be found.
         Resume Next
      Case Else
         MsgBox Err.Number & ": " & Err.Description, , "acbListFields"
   End Select
   Resume ExitHere
End Sub

Once acbListFields has completed its work, you can open the output table and use it any way you'd like. The sample frmListFields form displays the output table using a list box control.

This technique is easy to implement and offers more functionality than the built-in ListFields method. Many more (although not all of the possible) field properties are retrieved, and because acbListFields returns a table instead of a snapshot, you have added flexibility.

acbListFields doesn't decide which properties to write to the output table. Instead, it drives the process using the names of the fields in the output table. If you wish to collect a different set of properties, all you need to do is modify the code in acbMakeListFields and delete the output table (which will be recreated the next time you run acbListFields).

There is useful sample code behind the frmListFields form. Look at the GetTables function for an example of how to get a list of tables and queries and at the FillTables function for an example of a list-filling function (see the Solutions in Recipe 6.8 and Recipe 7.8 for more details on list-filling functions).

In your own applications, you may want to hide the output table in the database container. You can do this either by prefixing its name with "USys" or by checking the Hidden setting in the table's properties.

6.6.4 See Also

For more information on working with properties, see Recipe 7.9 in Chapter 7.