Creating a ForeignKeyConstraint Object

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Creating a ForeignKeyConstraint Object The ForeignKeyConstraint constructor is overloaded as follows: ForeignKeyConstraint(DataColumn parentDataColumn, DataColumn childDataColumn)

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Nội dung Text: Creating a ForeignKeyConstraint Object

Creating a ForeignKeyConstraint Object The ForeignKeyConstraint constructor is overloaded as follows: ForeignKeyConstraint(DataColumn parentDataColumn, DataColumn childDataColumn) ForeignKeyConstraint(DataColumn[] parentDataColumns, DataColumn[] childDataColumns) ForeignKeyConstraint(string constraintName, DataColumn parentDataColumn, DataColumn childDataColumn) ForeignKeyConstraint(string constraintName, DataColumn[] parentDataColumns, DataColumn[] childDataColumns) ForeignKeyConstraint(string constraintName, string parentDataTableName, string[] parentDataColumnNames, string[] childDataColumnNames, AcceptRejectRule acceptRejectRule, Rule deleteRule, Rule updateRule) where • parentDataColumn and parentDataColumns are the DataColumn objects in the parent DataTable. • childDataColumn and childDataColumns are the DataColumn objects in the child DataTable. • constraintName is the name you want to assign to the ConstraintName property of your ForeignKeyConstraint. • parentDataTableName is the name of the parent DataTable. • parentDataColumnNames and childDataColumnNames contain the names of the DataColumn objects in the parent and child DataTable objects. • acceptRejectRule, deleteRule, and updateRule are the various rules for the ForeignKey-Constraint. Earlier in the section "Creating a UniqueConstraint Object," you saw a code example that created two DataTable objects named customersDT and ordersDT. The following example creates a ForeignKeyConstraint object on the CustomerID DataColumn of ordersDT to the CustomerID DataColumn of customersDT: ForeignKeyConstraint myFKC = new ForeignKeyConstraint( "ForeignKeyConstraintCustomersOrders", customersDT.Columns["CustomerID"], ordersDT.Columns["CustomerID"] ); ordersDT.Constraints.Add(myFKC);
Notice that the ForeignKeyConstraint is added to ordersDT using the Add() method. Note To successfully add a ForeignKeyConstraint to a DataTable, each DataColumn value in the child DataTable must have a matching DataColumn value in the parent DataTable. The next example retrieves the constraint just added to ordersDT and displays its properties: myFKC = (ForeignKeyConstraint) ordersDT.Constraints["ForeignKeyConstraintCustomersOrders"]; Console.WriteLine("myFKC.AcceptRejectRule = " + myFKC.AcceptRejectRule); Console.WriteLine("Columns:"); foreach (DataColumn myDataColumn in myFKC.Columns) { Console.WriteLine("" + myDataColumn); } Console.WriteLine("myFKC.ConstraintName = " + myFKC.ConstraintName); Console.WriteLine("myFKC.DeleteRule = " + myFKC.DeleteRule); Console.WriteLine("RelatedColumns:"); foreach (DataColumn relatedDataColumn in myFKC.RelatedColumns) { Console.WriteLine(""+ relatedDataColumn); } Console.WriteLine("myFKC.RelatedTable = " + myFKC.RelatedTable); Console.WriteLine("myFKC.Table = " + myFKC.Table); Console.WriteLine("myFKC.UpdateRule = " + myFKC.UpdateRule); This example displays the following output: myFKC.AcceptRejectRule = None Columns: CustomerID myFKC.ConstraintName = ForeignKeyConstraintCustomersOrders myFKC.DeleteRule = Cascade RelatedColumns: CustomerID myFKC.RelatedTable = Customers myFKC.Table = Orders myFKC.UpdateRule = Cascade Note You'll find all the code examples shown in this section and the previous section,
"Creating a UniqueConstraint Object," in the AddConstraints.cs program. The listing is omitted from this book for brevity.