Name

UpdateRule [ForeignKeyConstraint only]

Synopsis

Rule rule = Constraint.UpdateRule;

Constraint.UpdateRule = rule;

Determines what happens if the parent’s key column is modified. You can use any value from the Rule enumeration, as shown in Table 26-3. The default is Cascade, which means that the child rows are updated to point to the new value.

Table 26-3. Rule values

Value	Description
Cascade	If the linked column is changed in the parent, the foreign key column in all child rows is updated accordingly.
None	No action is taken on child rows. Thus, if you change the linked column of a parent that has children, an exception is thrown. This is the traditional SQL Server behavior.
SetDefault	If the linked column of a parent row is changed, the foreign key column in the child rows is reset to the default value, if allowed (otherwise an exception is thrown).
SetNull	If the linked column of the parent row is changed, the foreign key column of all children is set to null. If the DataColumn.AllowDbNull property disallows this, an exception is thrown.

Example

In this example, all the child order records are updated to use the new CustomerID value:

// This is the ForeignKeyConstraint for the Orders table.

fkc.UpdateRule = Rule.Cascade;



// Select the first row.

DataRow row = ds.Tables["Customers"].Rows[0];



Console.WriteLine("Modifying: " + row["CustomerID"].ToString());



// Modify the CustomerID (all any linked order records will be updated).

row["CustomerID"] = "NEWCUST";