ADO.NET 3.5 Cookbook, 2nd Edition

2.7. Creating Single- and Multi-Column Primary Keys

Problem

You need to add a primary key to a table.

Solution

Either set the PrimaryKey property of the DataTable or add a primary key UniqueConstraint to the table.

The solution shows three techniques:

• Adding a one-column primary key by setting the PrimaryKey property of the DataTable.

• Adding a one-column primary key by creating a primary key UniqueConstraint and adding it to the constraints collection of the DataTable.

• Adding a two-column primary key by creating and adding a primary key UniqueConstraint directly to the DataTable.

In each case, information about the added primary key is output to the console.

The C# code in Program.cs in the project CreatePrimaryKey is shown in Example 2-7.

Example 2-7. File: Program.cs for CreatePrimaryKey solution

using System;
using System.Data;

namespace CreatePrimaryKey
{
    class Program
    {
        static void Main(string[] args)
        {
            // Create a table that will have a single-column constraint DataTable dt1 = new DataTable("Table-1"); // Add two columns DataColumn pkCol = dt1.Columns.Add("Id", typeof(int)); dt1.Columns.Add("Field1", typeof(string)).MaxLength = 50; // Set the primary key using the PrimaryKey dt1.PrimaryKey = new DataColumn[] { pkCol }; // Output the properties of the table constraint added OutputConstraintProperties(dt1); Console.WriteLine(); // Create a table that will have a single-column constraint DataTable dt2 = new DataTable("Table-2"); // Add two columns dt2.Columns.Add("Id", typeof(int)); dt2.Columns.Add("Field1", ...