System.Data Namespace

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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.

ForeignKeyConstraint Class Members

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Constructors Visibility Constructor Parameters public ForeignKeyConstraint ( DataColumn parentColumn , DataColumn childColumn ) public ForeignKeyConstraint ( String constraintName , DataColumn parentColumn , DataColumn childColumn ) public ForeignKeyConstraint ( DataColumn parentColumns , DataColumn childColumns ) public ForeignKeyConstraint ( String constraintName , DataColumn parentColumns , DataColumn childColumns ) public ForeignKeyConstraint ( String constraintName , String parentTableName , String parentColumnNames , String childColumnNames , AcceptRejectRule acceptRejectRule , Rule deleteRule , Rule updateRule ) public ForeignKeyConstraint ( String constraintName , String parentTableName , String parentTableNamespace , String parentColumnNames , String childColumnNames , AcceptRejectRule acceptRejectRule , Rule deleteRule , Rule updateRule )   Properties Visibility Name Value Type Accessibility public AcceptRejectRule AcceptRejectRule [ Get , Set ] public Columns DataColumn [ Get ] public DeleteRule Rule [ Get , Set ] public RelatedColumns DataColumn [ Get ] public RelatedTable DataTable [ Get ] public Table DataTable [ Get ] public UpdateRule Rule [ Get , Set ]   Methods Visibility Name Parameters Return Type public Equals ( Object key ) Boolean public GetHashCode ( ) Int32

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.

The following example initializes a ForeignKeyConstraint, sets various of its properties, and adds it to a DataTable object' s ConstraintCollection.

[ VB ]' the next line goes into the Declarations section of the module:
' suppliersProducts is a class derived from DataSet.
Private myDataSet As SuppliersProducts
Private Sub SetConstraint ( )
   ' 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 ( "SupplierFkConst", 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.Tables ( "Suppliers" ).Constraints.Add ( myFKC )
   myDataSet.EnforceConstraints = True
End Sub

Constraint   Constraints   ConstraintCollection   DataRelation   UniqueConstraint

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