System.Data Namespace


.NET Framework Class Library
Rule Enumeration

Indicates the action that occurs when a ForeignKeyConstraint is enforced.

Namespace:  System.Data
Assembly:  System.Data (in System.Data.dll)
Syntax
Visual Basic (Declaration) 
Public Enumeration Rule
Visual Basic (Usage) 
Dim instance As Rule
C# 
public enum Rule
Visual C++ 
public enum class Rule
JScript 
public enum Rule
Members
Member nameDescription
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkNoneNo action taken on related rows.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkCascadeDelete or update related rows. This is the default.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkSetNullSet values in related rows to DBNull.
Supported by the .NET Compact FrameworkSupported by the XNA FrameworkSetDefaultSet values in related rows to the value contained in the DefaultValue property.
Remarks

The Rule values are set to the UpdateRule and the DeleteRule properties of a ForeignKeyConstraint object found in a DataTable object's ConstraintCollection.

The Rule values determine the action that occurs when a value in a column is either deleted or updated. Of the two, deleting a value is the more critical and demanding of attention when setting a rule.

In the case where a value is deleted, Cascade specifies that all rows containing that value are also deleted. SetNull specifies that values in all child columns are set to null values. SetDefault specifies that all child columns be set to the default value for the column. None specifies that no action will occur, but exceptions are generated.

In the case where a value is updated, Cascade specifies that all child columns are likewise updated with the new value. SetNull specifies that all child columns be set to null values. SetDefault specifies that all child column values be set to the default value. None specifies that no action be taken, but exceptions are generated.

Constraints on a DataSet are not enforced unless the EnforceConstraints property is true.

When the AcceptChanges method is called, the AcceptRejectRule further determines what action occurs.
Examples
Visual Basic 
' 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
Platforms

Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune

The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
Version Information

.NET Framework

Supported in: 3.5, 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 3.5, 2.0, 1.0

XNA Framework

Supported in: 3.0, 2.0, 1.0
See Also

Reference

System.Data Namespace
Constraints
ForeignKeyConstraint
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