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 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

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role not supported), Windows Server 2003 SP2

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

Reference

ForeignKeyConstraint restringe la acción realizada cuando se elimina o actualiza un valor de columnas. Este tipo de restricción está pensado para utilizarlo con columnas de clave principal. En una relación primaria-secundaria entre dos tablas, la eliminación de un valor de la tabla primaria puede afectar las filas secundarias de una de las formas siguientes.

• También se pueden eliminar las filas secundarias (acción en cascada).

• Los valores de las columnas secundarias se pueden establecen en nulos.

• Los valores de las columnas secundarias se pueden establecer en predeterminados.

• Se puede generar una excepción.

Los objetos ForeignKeyConstraint están incluidos en el ConstraintCollection de un DataTable, al que se obtiene acceso mediante la propiedad Constraints.

Las restricciones no se fuerzan a menos que la propiedad EnforceConstraints esté establecida en true.

AcceptRejectRule se fuerza siempre que se invoca el método AcceptChanges de un objeto DataTable.

En el ejemplo siguiente se crea un ForeignKeyConstraint, se establecen algunas de sus propiedades y se agrega a un ConstraintCollection de un objeto DataTable.

' 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

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 o posterior, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (no se admite Server Core), Windows Server 2008 R2 (se admite Server Core con SP1 o posterior), Windows Server 2003 SP2

Este tipo es seguro para operaciones de lectura multiproceso. Debe sincronizar cualquier operación de escritura.

Referencia