C# SQL when/how do I close the connection?

Question

I was using this code:

public class SQLConnection : IConnection
{
    private SqlConnection _sqlConnection = null;

    //bunch of interface implementations for my project

    //the destructor
    ~SQLConnection()
    {
        if(_sqlConnection != null)
        {
            if(_sqlConnection.State == ConnectionState.Open)
            {
                _sqlConnection.Close();
            }
            _sqlConnection.Dispose();
        }
    }
}

This was working well until some time ago, when I started receiving this error: Internal .Net Framework Data Provider error 1

After googling a bit, I found this link (the Caution part) and I think that's what's happening to me. My class was managing the connection state opening and closing each time, but now that it seems I can't manage it this way, is there any other way that I can do this without having to go to every function that I use the connection and call connection.Close() explicitly?

Answer 1

Always use 'using' for safely disposing the connections.

using(var _sqlConnection = new SqlConnection())
{
     //code here
     _sqlConnection.Open();
}


//Safely disposed.

Also, it is never a good idea to use destructor explicitly in C# code unless you have unmanaged code.

Answer 2

You're probably receiving this error when one code is trying to access SQLConnection that has been already garbage collected. This usually will happen in cases like this one

 SqlConnection sqlConn;

 using (var sqlConnection = new SqlConnection())
 {
    sqlConn = sqlConnection;
    sqlConnection.Open();
 }

 sqlConn.Close();

I know this example looks silly as it's overly simplified, but it happens often when programmers tend to share a connection object between Managing Classes. Look for any recent changes in your code. Maybe you're passing an instance of a connection between multiple objects. One of those objects gets Garbage Collected and in turn the connection gets disposed too.