NGWS SDK Documentation  

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DataTable.Constraints

Gets the collection of constraints maintained by this table.

[Visual Basic]
Public ReadOnly Property Constraints As ConstraintsCollection
[C#]
public ConstraintsCollection Constraints {get;}
[C++]
public: __property ConstraintsCollection* get_Constraints();
[JScript]
public function get Constraints() : ConstraintsCollection;

Property Value

A ConstraintsCollection that contains the collection of Constraint objects for the table.

Remarks

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.

A UniqueConstraint becomes active when attempting to set a value in a primary key to a non-unique value.

Example [Visual Basic]

The following example adds a ForeignKeyConstraint to the collection of constraints.

[Visual Basic]

' The next line goes into the Declarations section of the module:
' SuppliersProducts is a class derived from DataSet.
Private myDataSet As SuppliersProducts 


Private Sub CreateConstraint()
   Dim myFKC As ForeignKeyConstraint
   myFKC = New ForeignKeyConstraint _
      (myDataSet.Tables("Suppliers"), _
      myDataSet.Tables("Suppliers").Columns("CompanyID"), _
      myDataSet.Tables("Products"), _
      myDataSet.Tables("Products").Columns("CompanyID"))
   ' Set null values when a value is deleted.
   myFKC.DeleteRule = Rule.SetNull
   myFKC.UpdateRule = Rule.Cascade
   myFKC.AcceptRejectRule = AcceptRejectRule.Cascade

   myDataSet.Tables("Suppliers").Constraints.Add myFKC
   myDataSet.EnforceConstraints = True
   
End Sub

See Also

DataTable Class | DataTable Members | System.Data Namespace | AcceptRejectRule | ForeignKeyConstraint | UniqueConstraint | Rule