Question

Does SqlDataAdapter close the SqlConnection after the Fill() function or do I need close it myself?

string cnStr = @"Data Source=TEST;Initial Catalog=Suite;Persist Security Info=True;User ID=app;Password=Immmmmm";
cn = new SqlConnection(cnStr);
SqlCommand cmd = new SqlCommand("SELECT TOP 10 * FROM Date", cn);
SqlDataAdapter adapter = new SqlDataAdapter(cmd);

DataSet ds = new DataSet();
adapter.Fill(ds);

cn.Close() // ????????

Console.WriteLine(ds.Tables[0].Rows.Count);
Console.WriteLine(cn.State);

Answer 1

In your current usage, it will close for you:

If the IDbConnection
is closed before Fill is called, it is opened to retrieve data and
then closed. If the connection is open before Fill is called, it
remains open.

http://msdn.microsoft.com/en-us/library/zxkb3c3d.aspx

I think it’s always better to explicitly cater for it yourself with a using statement:

using (SqlConnection conn = new SqlConnection(""))
{
    conn.Open();

    // Do Stuff.

} // Closes here on dispose.

This is often more readable and doesn’t rely on people understanding the inner workings of SqlDataAdapter.Fill, just the using statement and connections.

However, if you know the connection is closed before the adapter uses it (as in, you’ve just created the connection) and it’s not used for anything else, your code is perfectly safe and valid.

Personally, I’d write something like this:

    string cnStr = "Data Source=TEST;Initial Catalog=Suite;Persist Security Info=True;User ID=app;Password=Immmmmm";
    DataSet ds = new DataSet();

    using (SqlConnection cn = new SqlConnection(cnStr))
    using (SqlCommand cmd = new SqlCommand("SELECT TOP 10 * FROM Date", cn))
    using (SqlDataAdapter adapter = new SqlDataAdapter(cmd))
    { 
        conn.Open();
        adapter.Fill(ds);       
    }