Was this page helpful?
Your feedback about this content is important. Let us know what you think.
Additional feedback?
1500 characters remaining
ForeignKeyConstraint Class
Collapse the table of content
Expand the table of content

ForeignKeyConstraint Class

Represents an action restriction enforced on a set of columns in a primary key/foreign key relationship when a value or row is either deleted or updated.

For a list of all members of this type, see ForeignKeyConstraint Members.


[Visual Basic]
Public Class ForeignKeyConstraint
   Inherits Constraint
public class ForeignKeyConstraint : Constraint
public __gc class ForeignKeyConstraint : public Constraint
class ForeignKeyConstraint extends Constraint

Thread Safety

This type is safe for multithreaded read operations. You must synchronize any write operations.


A ForeignKeyConstraint restricts the action performed when a value in a column (or columns) is either deleted or updated. Such a constraint is intended to be used with primary key columns. In a parent/child relationship between two tables, deleting a value from the parent table can affect the child rows in one of the following ways.

  • The child rows can also be deleted (a cascading action).
  • The values in the child column (or columns) can be set to null values.
  • The values in the child column (or columns) can be set to default values.
  • An exception can be generated.

ForeignKeyConstraint objects are contained in the ConstraintCollection of a DataTable, which is accessed through the Constraints property.

Constraints are not enforced unless the EnforceConstraints property is set to true.

The AcceptRejectRule is enforced whenever a DataTable object's AcceptChanges method is invoked.


[Visual Basic] The following example creates a ForeignKeyConstraint, sets some of its properties, and adds it to a DataTable object's ConstraintCollection.

[Visual Basic] 
' The next line goes into the Declarations section of the module:
' SuppliersProducts is a class derived from DataSet.
Private myDataSet As SuppliersProducts  

Private Sub CreateConstraint()
   ' Declare parent column and child column variables.
   Dim pCol As DataColumn
   Dim cCol As DataColumn
   Dim myFKC As ForeignKeyConstraint
   ' Set parent and child column variables.
   pCol = MyDataSet.Tables("Suppliers").Columns("SupplierID")
   cCol = MyDataSet.Tables("Products").Columns("SupplierID")
   myFKC = New ForeignKeyConstraint("SupplierFKConstraint", pCol, cCol)
   ' Set null values when a value is deleted.
   myFKC.DeleteRule = Rule.SetNull
   myFKC.UpdateRule = Rule.Cascade
   myFKC.AcceptRejectRule = AcceptRejectRule.Cascade
   ' Add the constraint, and set EnforceConstraints to true.
   myDataSet.EnforceConstraints = True
End Sub

[C#, C++, JScript] No example is available for C#, C++, or JScript. To view a Visual Basic example, click the Language Filter button Language Filter in the upper-left corner of the page.


Namespace: System.Data

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework

Assembly: System.Data (in System.Data.dll)

See Also

ForeignKeyConstraint Members | System.Data Namespace | AcceptRejectRule | DataTable | ConstraintCollection | Rule

© 2015 Microsoft