Essential ADO.NET

3.2. Connection Classes

The connection classes (SqlConnection and OleDbConnection) are not built around a common base class structure; instead, they're built around implementation of a common interface, IDbConnection. You must instantiate a concrete class of the correct type, although it can be cast to the IDbConnection interface:

IDbConnection conn = new SqlConnection();
IDbConnection oconn = new OleDbConnection();

As in ADO classic (also known as ADODB), you can explicitly create and control the Connection instances, or you can pass a connection string as a constructor parameter to other objects, such as the DataAdapter, in lieu of a Connection instance. If a connection string is passed to the DataAdapter's constructor, it implicitly creates ...