In the process of many of the projects I have done, I have always had a unresolved issue in troubled me, that is the development of persistence. The development of persistence layers is generally either with CMP or use JDBC DAO. CMP does not have to be said, it is a failed practice for me, and JDBC Dao has a lot of difficulties. I am very difficult to make the relationship of the relationship table to the relationship of the lasting object, which is mainly reflected. The relationship between the multi-table cannot be directly mapped to the map of the persistent object, which may be a table mapping multiple persistent objects, which may be multiple tables to map a persistent object, and some of the tables are mapped to one Persistent objects, but other fields are mapped to other persistent objects. And even if these problems are processed, you can't program a lasting object (PO) in the way, because there is a 1: n relationship's persistent object's query is actually 1 N times to the database of SQL, I have A failure layer design, the result is that a query of a lot of other lasting objects is 5N 1 time SQL, the speed is slow, and finally, the entire modification of the underlying design is completely abandoned, it is completely abandoned. Follow the table fields.
