Does closing a database connection in Dispose method is right?

Question

I've had a suspicion that a database connection used in one of our applications is not always closed. I went to see the code and I've found a class DataProvider that has SqlConnection object. The connection is opened in the constructor of this class and closed in it's Dispose method (don't judge that, i know keeping an open connection is evil, it's just not my code and it's not the point of the question anyway). Dispose method is implemented like this:

protected virtual void Dispose(bool disposing)
        {
            if (!_disposed)
            {
                if (disposing)
                {
                    if (_conn != null)
                        _conn.Close();
                }

                _disposed = true;
            }
        }

The question is: does it always guarantee that the connection is closed? And is this code right? I think there should be _conn.Dispose() called - am I right and could it affect not closing the connection (probably not)?

Answer 1

I think you should take it to your destructor method, and you should add a line that checks if the connection is not closed :

class YourClass
{
    ~YourClass()
    {
        if (_conn != null && _conn.State != ConnectionState.Closed )
        {
            _conn.Close();
        }
    }
}

Here is a paragraph on using dispose or destructor from MSDN :

If your application is using an expensive external resource, we also recommend that you provide a way to explicitly release the resource before the garbage collector frees the object. You do this by implementing a Dispose method from the IDisposable interface that performs the necessary cleanup for the object. This can considerably improve the performance of the application. Even with this explicit control over resources, the destructor becomes a safeguard to clean up resources if the call to the Dispose method failed.

Answer 2

conn.Dispose(); will also close the connection, so can't hurt changing it to follow the dispose pattern.

But there functionally equivalent so there must be a problem else where.

http://msdn.microsoft.com/en-us/library/system.data.sqlclient.sqlconnection.close.aspx

If the SqlConnection goes out of scope, it won't be closed. Therefore, you must explicitly close the connection by calling Close or Dispose. Close and Dispose are functionally equivalent. If the connection pooling value Pooling is set to true or yes, the underlying connection is returned back to the connection pool. On the other hand, if Pooling is set to false or no, the underlying connection to the server is closed.

Answer 3

Dispose is never called automatically.

The connection will not be closed until the Dispose method of your object is explicitly called, or if your class in used in a using() block

A safer way is to call the dispose method in your finalizer and ensure the finalizer is suppressed when the Dispose method is called.

This article present the correct way to implement the pattern

Hope it helps !

Cédric