Question

Which pattern is better for SqlConnection object? Which is better in performance?
Do you offer any other pattern?

class DataAccess1 : IDisposable
{
    private SqlConnection connection;

    public DataAccess1(string connectionString)
    {
        connection = new SqlConnection(connectionString);
    }

    public void Execute(string query)
    {
        using (SqlCommand command = connection.CreateCommand())
        {
            command.CommandText = query;
            command.CommandType = CommandType.Text;
            // ...

            command.Connection.Open();
            command.ExecuteNonQuery();
            command.Connection.Close();
        }
    }

    public void Dispose()
    {
        connection.Dispose();
    }
}

VS

class DataAccess2 : IDisposable
{
    private string connectionString;

    public DataAccess2(string connectionString)
    {
        this.connectionString = connectionString;
    }

    public void Execute(string query)
    {
        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            SqlCommand command = connection.CreateCommand();
            command.CommandText = query;
            command.CommandType = CommandType.Text;
            // ...

            command.Connection.Open();
            command.ExecuteNonQuery();
            command.Connection.Close();
        }
    }

    public void Dispose()
    {            
    }
}

Answer 1

Suggest going with DataAccess2. It’s a personal preference though. Some might even suggest your class be static. It’d be difficult to say that one is more performant than the other. You’re on the path of IDisposable, which is great.

I’d be happy to read and maintain both styles shown above in your question.

Consider having your DAL be able to read the connection string from a .config as well, rather than exclusively allowing the value to be passed in the constructor.

public DataAccess2(string connStr)
{
    this.connectionString = connStr;
}
public DataAccess2()
{
    this.connectionString = 
            ConfigurationManager.ConnectionStrings["foo"].ConnectionString;
}

Consider wrapping your SqlCommand in a using as well.

using (var conn = new SqlConnection(connectionString))
{
    using(var cmd = conn.CreateCommand())
    {

    }
}