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Field Object

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Access Developer Reference

A Field object represents a column of data with a common data type and a common set of properties.

Remarks

The Fields collections of Index, QueryDef, Relation, and TableDef objects contain the specifications for the fields those objects represent. The Fields collection of a Recordset object represents the Field objects in a row of data, or in a record. You use the Field objects in a Recordset object to read and set values for the fields in the current record of the Recordset object.

In a Microsoft Access workspacee, you manipulate a field using a Field object and its methods and properties. For example, you can:

  • Use the OrdinalPosition property to set or return the presentation order of the Field object in a Fields collection.
  • Use the Value property of a field in a Recordset object to set or return stored data.
  • Use the AppendChunk and GetChunk methods and the FieldSize property to get or set a value in an OLE Object or Memo field of a Recordset object.
  • Use the Type, Size, and Attributes properties to determine the type of data that can be stored in the field.
  • Use the SourceField and SourceTable properties to determine the original source of the data.
  • Use the ForeignName property to set or return information about a foreign field in a Relation object.
  • Use the AllowZeroLength, DefaultValue, Required, ValidateOnSet, ValidationRule, or ValidationText properties to set or return validation conditions.
  • Use the DefaultValue property of a field on a TableDef object to set the default value for this field when new records are added.

To create a new Field object in an Index, TableDef, or Relation object, use the CreateField method.

When you access a Field object as part of a Recordset object, data from the current record is visible in the Field object's Value property. To manipulate data in the Recordset object, you don't usually reference the Fields collection directly; instead, you indirectly reference the Value property of the Field object in the Fields collection of the Recordset object.

To refer to a Field object in a collection by its ordinal number or by its Name property setting, use any of the following syntax forms:

Fields(0)

Fields("name")

Fields![name]

With the same syntax forms, you can also refer to the Value property of a Field object that you create and append to a Fields collection. The context of the field reference will determine whether you are referring to the Field object or the Value property of the Field object.

Example

This example shows what properties are valid for a Field object depending on where the Field resides (for example, the Fields collection of a TableDef, the Fields collection of a QueryDef, and so forth). The FieldOutput procedure is required for this procedure to run.

Visual Basic for Applications 
  Sub FieldX()

Dim dbsNorthwind As Database
Dim rstEmployees As Recordset
Dim fldTableDef As Field
Dim fldQueryDef As Field
Dim fldRecordset As Field
Dim fldRelation As Field
Dim fldIndex As Field
Dim prpLoop As Property


Set dbsNorthwind = OpenDatabase("Northwind.mdb")
Set rstEmployees = _
dbsNorthwind.OpenRecordset("Employees")


' Assign a Field object from different Fields
' collections to object variables.
Set fldTableDef = _
dbsNorthwind.TableDefs(0).Fields(0)
Set fldQueryDef =dbsNorthwind.QueryDefs(0).Fields(0)
Set fldRecordset = rstEmployees.Fields(0)
Set fldRelation =dbsNorthwind.Relations(0).Fields(0)
Set fldIndex = _
dbsNorthwind.TableDefs(0).Indexes(0).Fields(0)


' Print report.
FieldOutput "TableDef", fldTableDef
FieldOutput "QueryDef", fldQueryDef
FieldOutput "Recordset", fldRecordset
FieldOutput "Relation", fldRelation
FieldOutput "Index", fldIndex


rstEmployees.Close
dbsNorthwind.Close


End Sub


Sub FieldOutput(strTemp As String, fldTemp As Field)
' Report function for FieldX.


Dim prpLoop As Property


Debug.Print "Valid Field properties in " & strTemp


' Enumerate Properties collection of passed Field
' object.
For Each prpLoop In fldTemp.Properties
' Some properties are invalid in certain
' contexts (the Value property in the Fields
' collection of a TableDef for example). Any
' attempt to use an invalid property will
' trigger an error.
On Error Resume Next
Debug.Print "  " & prpLoop.Name & " = " & _
prpLoop.Value
On Error GoTo 0
Next prpLoop


End Sub

This example uses the CreateField method to create three Fields for a new TableDef. It then displays the properties of those Field objects that are automatically set by the CreateField method. (Properties whose values are empty at the time of Field creation are not shown.)

Visual Basic for Applications 
  Sub CreateFieldX()

Dim dbsNorthwind As Database
Dim tdfNew As TableDef
Dim fldLoop As Field
Dim prpLoop As Property


Set dbsNorthwind = OpenDatabase("Northwind.mdb")


Set tdfNew = dbsNorthwind.CreateTableDef("NewTableDef")


' Create and append new Field objects for the new
' TableDef object.
With tdfNew
' The CreateField method will set a default Size
' for a new Field object if one is not specified.
.Fields.Append .CreateField("TextField", dbText)
.Fields.Append .CreateField("IntegerField", dbInteger)
.Fields.Append .CreateField("DateField", dbDate)
End With


dbsNorthwind.TableDefs.Append tdfNew


Debug.Print "Properties of new Fields in " & tdfNew.Name


' Enumerate Fields collection to show the properties of
' the new Field objects.
For Each fldLoop In tdfNew.Fields
Debug.Print "  " & fldLoop.Name


  For Each prpLoop In fldLoop.Properties
     ' Properties that are invalid in the context of
     ' TableDefs will trigger an error if an attempt
     ' is made to read their values.
     On Error Resume Next
     Debug.Print "    " & prpLoop.Name & " - " & _
        IIf(prpLoop = "", "[empty]", prpLoop)
     On Error GoTo 0
  Next prpLoop



Next fldLoop


' Delete new TableDef because this is a demonstration.
dbsNorthwind.TableDefs.Delete tdfNew.Name
dbsNorthwind.Close


End Sub

See Also