Question

I have a data access layer namespace that has a lot of repeated code (mostly setting up command objects and executing stored procedures to return data sets that get added to Lists). I’m trying to write a generic factory method that returns a List<T>. I’m relatively new to both generics and delegates. My thought was to have a Func parameter that creates the objects that get added to the List<T>. It would be called within the usual while dataReader.Read() block. My problem is, the data sets I’ll be working with have varying numbers of columns.

Here is what I have so far:

private static List<T> ListFromDatabase<T,U>(String CommandName, SqlConnection SqlConn, Func<T,U> CreateListObj, 
    List<SqlParameter> ParamList = null)
{
    List<T> returnList = new List<T>();

    using (SqlCommand cmd = new SqlCommand(CommandName,SqlConn))
    {
        cmd.CommandType = CommandType.StoredProcedure;
        foreach (SqlParameter sp in ParamList)
        {
            if (sp.Value == null)
                sp.Value = DBNull.Value;
            cmd.Parameters.Add(sp);
        }

        SqlDataReader sdr = cmd.ExecuteReader();
        while (sdr.Read())
        {
            returnList.Add(CreateListObj);
        }
    }

    return returnList;
}

At my current level of understanding, this may not be possible since I would likely have to vary the Func signature for varying numbers of parameters. Is this do- able, or close? If not I’m open to a different approach, if anyone can help. Many thanks in advance..

Update: This is exactly what I was looking for:

Convert rows from a data reader into typed results

Answer 1

Why not pass your SqlDataReader to your delegate as an IDataRecord? The delegate can get what it needs from the data record; you maintain control over iterating over the reader.