Tài liệu Creating a ForeignKeyConstraint Object doc

Creating a ForeignKeyConstraint Object The ForeignKeyConstraint constructor is overloaded as follows: ForeignKeyConstraintDataColumn parentDataColumn, DataColumn childDataColumn ForeignK

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