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Showing content from https://docs.microsoft.com/en-us/dotnet/api/system.data.foreignkeyconstraint below:

ForeignKeyConstraint Class (System.Data) | Microsoft Learn

ForeignKeyConstraint Class Definition

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.

public ref class ForeignKeyConstraint : System::Data::Constraint

public class ForeignKeyConstraint : System.Data.Constraint

[System.Serializable]
public class ForeignKeyConstraint : System.Data.Constraint

type ForeignKeyConstraint = class
    inherit Constraint

[<System.Serializable>]
type ForeignKeyConstraint = class
    inherit Constraint

Public Class ForeignKeyConstraint
Inherits Constraint

Inheritance

Attributes

Examples

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

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.

Constructors ForeignKeyConstraint(DataColumn, DataColumn)

Initializes a new instance of the ForeignKeyConstraint class with the specified parent and child DataColumn objects.

ForeignKeyConstraint(DataColumn[], DataColumn[])

Initializes a new instance of the ForeignKeyConstraint class with the specified arrays of parent and child DataColumn objects.

ForeignKeyConstraint(String, DataColumn, DataColumn)

Initializes a new instance of the ForeignKeyConstraint class with the specified name, parent and child DataColumn objects.

ForeignKeyConstraint(String, DataColumn[], DataColumn[])

Initializes a new instance of the ForeignKeyConstraint class with the specified name, and arrays of parent and child DataColumn objects.

ForeignKeyConstraint(String, String, String, String[], String[], AcceptRejectRule, Rule, Rule)

This constructor is provided for design time support in the Visual Studio environment. ForeignKeyConstraint objects created by using this constructor must then be added to the collection via AddRange(Constraint[]). Tables and columns with the specified names must exist at the time the method is called, or if BeginInit() has been called prior to calling this constructor, the tables and columns with the specified names must exist at the time that EndInit() is called.

ForeignKeyConstraint(String, String, String[], String[], AcceptRejectRule, Rule, Rule)

Properties Methods Thread Safety

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