I am working on a C# project that is pulling data from SQL Server, ODBC data-sources and Oracle Databases at different times.

At this point, I have created 3 different classes - Once for each type of DB access. However, I am seeing that 95% of the code is identical between each of the libraries - The main difference being in creating the Connection and Command objects.

As a VERY simple example of what's in the classes, here could be an example:

public class Oracle
{
    static DataTable exec_DT(string query, string conn_str)
    {
        DataTable retVal = new DataTable();

        using (OracleConnection conn = new OracleConnection(conn_str))
            using (OracleCommand cmd = new OracleCommand(query, conn))
            {
                conn.Open();
                using (OracleDataReader rdr = cmd.ExecuteReader())
                {
                    retVal.Load(rdr);
                    rdr.Close();
                }
            }

        return retVal;
    }
}

and

public class SQLServer
{
    static DataTable exec_DT(string query, string conn_str)
    {
        DataTable retVal = new DataTable();

        using (SqlConnection conn = new SqlConnection(conn_str))
        using (SqlCommand cmd = new SqlCommand(query, conn))
        {
            conn.Open();
            using (SqlDataReader rdr = cmd.ExecuteReader())
            {
                retVal.Load(rdr);
                rdr.Close();
            }
        }

        return retVal;
    }
}

Basically, I need to get the same kind of return data frmo each of my databases and the methods to do so are near-identical, the difference being the Connection and Command-type objects.

Now, when I look at both connection objects, I see that they both inherit from DbConnection:

public sealed class SqlConnection : DbConnection, ICloneable

public sealed class OracleConnection : DbConnection, ICloneable

But I still can't think of a good way to create a generic / abstract parent class that can stop the need for this kind of code duplication as the DBConnection / DBCommand classes are abstract and, when I try something along the following lines:

using (DbConnection conn = new DbConnection(conn_str))
using (DbCommand cmd = new DbCommand(query, conn))

I get errors such as Cannot create an instance of the abstract class or interface 'System.Data.Common.DbCommand'

I'm very much a newbie and any help / sample code / links to ways this has been done well in the past would really be greatly appreciated!

THANKS!!!