Tài liệu Creating a UniqueConstraint Object ppt

Creating a UniqueConstraint Object

In this section, you'll learn how to create a UniqueConstraint object. The

UniqueConstraint constructor is overloaded as follows:

UniqueConstraint(DataColumn myDataColumn)

UniqueConstraint(DataColumn[] myDataColumns)

UniqueConstraint(DataColumn myDataColumn, bool isPrimaryKey)

UniqueConstraint(DataColumn[] myDataColumns, bool isPrimaryKey)

UniqueConstraint(string constraintName, DataColumn myDataColumn)

UniqueConstraint(string constraintName, DataColumn[] myDataColumns)

UniqueConstraint(string constraintName, DataColumn myDataColumn, bool

isPrimaryKey)

UniqueConstraint(string constraintName, DataColumn[] myDataColumns,

bool isPrimaryKey)

UniqueConstraint(string constraintName, string[] columnNames,

bool isPrimaryKey)

where

• myDataColumn and myDataColumns are the DataColumn objects that you want

to ensure are unique.

• constraintName is the name you want to assign to the ConstraintName property of

your UniqueConstraint.

• isPrimaryKey indicates whether your UniqueConstraint is for a primary key.

Before creating and adding a UniqueConstraint to a DataTable, you first need a

DataTable. The following example creates and populates two DataTable objects named

customersDT and ordersDT (the ordersDT object will be used later in the section

"Creating a ForeignKeyConstraint Object"):

SqlCommand mySqlCommand = mySqlConnection.CreateCommand();

mySqlCommand.CommandText =

"SELECT CustomerID, CompanyName " +

"FROM Customers " +

"WHERE CustomerID = 'ALFKI'" +

"SELECT OrderID, CustomerID " +

"FROM Orders " +

"WHERE CustomerID = 'ALFKI';";

SqlDataAdapter mySqlDataAdapter = new SqlDataAdapter();

mySqlDataAdapter.SelectCommand = mySqlCommand;