In order to support several DBMS brands with adapter we need a solution for mapping System.Guid to SQLServer, mySQL and Oracle.

If find out a lot of theads a long time ago to that problem.

How can I map a PK Field in mySQL. I have tried several datatypes varchar(3 , varbinary and blob.

If I take the varchar(3 , i can save the data in the mySQL database, but i can't read because the cast conversion failed.

Has somebody solved this problem?

Have you checked TypeConverters ? Please check "Concepts -> Type Converters" in the docs.