DB Polymorphism

[Ultra]

Hi Export,

I want to write a class to deal with all db tier with different platform,
but when I using a DbAdapter (superclass) pointer to point a OleDBAdapter
(subclasse) instance, it said the selectCommand is protected.
How can I do that polymorphism?

below is my class:
public class db
{
protected System.Componen tModel.Componen t dbCon;
protected System.Data.Com mon.DbDataAdapt er dbDataAdapter;
protected string dbType;

public db(String dbType, string ConnectionStr)
{
//
// TODO: Add constructor logic here
//
switch (dbType)
{
case "mysql":
dbCon = new System.Data.Odb c.OdbcConnectio n(ConnectionStr );
dbDataAdapter = new System.Data.Odb c.OdbcDataAdapt er();
break;
default:
dbCon = new System.Data.Ole Db.OleDbConnect ion(ConnectionS tr);
dbDataAdapter = new System.Data.Ole Db.OleDbDataAda pter();
break;
};

this.dbType = dbType;
}

public DataSet setSelectComman d(string sql)
{
DataSet rs = new DataSet();

this.dbDataAdap ter.SelectComma nd.Connection = dbCon;
this.dbDataAdap ter.SelectComma nd.CommandText = sql;
this.dbDataAdap ter.Fill(rs);

return rs;
}
}