c# - Is it necessary to manually close and dispose of SqlDataReader?

Question

I'm working with legacy code here and there are many instances of SqlDataReader that are never closed or disposed. The connection is closed but, I am not sure if it is necessary to manage the reader manually.

Could this cause a slowdown in performance?

Answer 1

Try to avoid using readers like this:

SqlConnection connection = new SqlConnection("connection string");
SqlCommand cmd = new SqlCommand("SELECT * FROM SomeTable", connection);
SqlDataReader reader = cmd.ExecuteReader();
connection.Open();
if (reader != null)
{
      while (reader.Read())
      {
              //do something
      }
}
reader.Close(); // <- too easy to forget
reader.Dispose(); // <- too easy to forget
connection.Close(); // <- too easy to forget

Instead, wrap them in using statements:

using(SqlConnection connection = new SqlConnection("connection string"))
{

    connection.Open();

    using(SqlCommand cmd = new SqlCommand("SELECT * FROM SomeTable", connection))
    {
        using (SqlDataReader reader = cmd.ExecuteReader())
        {
            if (reader != null)
            {
                while (reader.Read())
                {
                    //do something
                }
            }
        } // reader closed and disposed up here

    } // command disposed here

} //connection closed and disposed here

The using statement will ensure correct disposal of the object and freeing of resources.

If you forget then you are leaving the cleaning up to the garbage collector, which could take a while.