Question

What is best practice for C# Window Forms and SQL connection instance. I need the same SQL connection in all window forms. What is best implementation practice for this? Where do I put the SQL connection?

I am using Compact framework 3.5.

Answer 1

Personally I prefer to leave connection management to the ADO.NET connection pool and everytime I want to query:

using (var conn = new SqlConnection("connection string"))
using (var cmd = conn.CreateCommand())
{
    conn.Open();
    cmd.CommandText = "SELECT id FROM foo;";
    using (var reader = cmd.ExecuteReader())
    {
        while (reader.Read())
        {
            // ...
        }
    }
}

When you call conn.Open() a physical connection is not opened, it is drawn from the connection pool, and when the using block end and invokes .Dispose the connection is not closed but returned to the connection pool in order to be reused. This improves performance and relieves me from worrying about where to put or store those SqlConnection instances in applications.