SqlConnection. The C# SqlConnection class handles database connections. It initiates a connection to your SQL database. This class is best used in a using resource acquisition statement.

More details. We call Open to query the database with SqlCommand. With System.Data.SqlClient classes, we often use many together (like SqlParameter, SqlDataReader).

SqlCommand

SqlClient

SqlDataReader

OdbcConnection

First example. We use SqlConnection in a "using" statement. The SqlConnection has a constructor that requires a string reference pointing to the connection string character data.

using System;
using System.Data.SqlClient;

class Program
{
    static void Main()
    {
        //
        // First access the connection string.
        //
        string connectionString = ConsoleApplication1.Properties.Settings.Default.ConnectionString;
        //
        // In a using statement, acquire the SqlConnection as a resource.
        //
        using (SqlConnection con = new SqlConnection(connectionString))
        {
            //
            // Open the SqlConnection.
            //
            con.Open();
            //
            // This code uses an SqlCommand based on the SqlConnection.
            //
            using (SqlCommand command = new SqlCommand("SELECT TOP 2 * FROM Dogs1", con))
            using (SqlDataReader reader = command.ExecuteReader())
            {
                while (reader.Read())
                {
                    Console.WriteLine("{0} {1} {2}", reader.GetInt32(0), reader.GetString(1), reader.GetString(2));
                }
            }
        }
    }
}
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Program notes. This program will not work unless you change the connection string reference to point to a correct one in your environment.

using

Open method call. The using statement creates a read-only variable of type SqlConnection. You need to call Open() on the SqlConnection instance before using it in an SqlCommand.

Summary. We looked at database code. We stressed the proper usage of the SqlConnection class and the resource acquisition pattern.