ForeignKeyConstraint Class
Assembly: System.Data (in system.data.dll)
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.
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The child rows can also be deleted (a cascading action).
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The values in the child column (or columns) can be set to null values.
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The values in the child column (or columns) can be set to default values.
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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 creates a ForeignKeyConstraint, sets some of its properties, and adds it to a DataTable object's ConstraintCollection.
' The next line goes into the Declarations section of the module: ' SuppliersProducts is a class derived from DataSet. Private suppliersProducts As SuppliersProducts Private Sub CreateConstraint() ' Declare parent column and child column variables. Dim parentColumn As DataColumn Dim childColumn As DataColumn Dim fkeyConstraint As ForeignKeyConstraint ' Set parent and child column variables. parentColumn = suppliersProducts.Tables("Suppliers").Columns("SupplierID") childColumn = suppliersProducts.Tables("Products").Columns("SupplierID") fkeyConstraint = New ForeignKeyConstraint( _ "SupplierFKConstraint", parentColumn, childColumn) ' Set null values when a value is deleted. fkeyConstraint.DeleteRule = Rule.SetNull fkeyConstraint.UpdateRule = Rule.Cascade fkeyConstraint.AcceptRejectRule = AcceptRejectRule.Cascade ' Add the constraint, and set EnforceConstraints to true. suppliersProducts.Tables("Products").Constraints.Add(fkeyConstraint) suppliersProducts.EnforceConstraints = True End Sub
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The .NET Framework does not support all versions of every platform. For a list of the supported versions, see System Requirements.