對應生成的DDL drop table PARENT; 代碼: drop table CHILD; create table PARENT (ID INTEGER not null generated by default as identity, PRimary key (ID)); create table CHILD (ID INTEGER not null generated by default as identity, PARENTID INTEGER, primary key (ID)); alter table CHILD add constraint FK3D1FCFC74B18345 foreign key (PARENTID) references PARENT;
代碼: drop table PARENT; drop table CHILD; create table PARENT (ID INTEGER not null generated by default as identity, primary key (ID)); create table CHILD (ID INTEGER not null generated by default as identity, PARENTID INTEGER, primary key (ID)); alter table CHILD add constraint FK3D1FCFC74B18345 foreign key (PARENTID) references PARENT;
代碼: ITxMgr tx = null; tx = HibernateTxMgr.beginTrans("Add a new relationships..."); session = (Session) tx.getSession(); parent = new ParentPO(); ChildPO child = new ChildPO(parent); ChildPO child2 = new ChildPO(parent); List list = new ArrayList(); list.add(child); list.add(child2); parent.setChildren(list); session.save(parent); session.flush(); System.out.println("dddddddddddddddddddddddddddddddddddddddddddddddddddddd") ; ChildPO child3 = new ChildPO(); child3.setParent(parent); session.save(child3); session.flush(); System.out.println("eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee") ; tx.endTrans();
hibernate 生成的sql Hibernate: insert into PARENT (ID) values (default)
代碼: Hibernate: insert into CHILD (PARENTID, ID) values (?, default)
Hibernate: insert into CHILD (PARENTID, ID) values (?, default)
Hibernate: update CHILD set PARENTID=? where ID=? dddddddddddddddddddddddddddddddddddddddddddddddddddddd Hibernate: insert into CHILD (PARENTID, ID) values (?, default) Hibernate: values IDENTITY_VAL_LOCAL()
結果 C:/Myapp/SQLLIB/BIN>db2 select * from parent
代碼: ID ----------- 46 ID PARENTID ----------- ----------- 77 46 78 46 79 46
明顯比原來多了一句Hibernate: update CHILD set PARENTID=? where ID=?針對每一個孩子都去更新父親的id明顯速度很慢，因為父親有個孩子的集合，他無法知道哪個孩子的父親id已經指向自己了,所以對于每一個孩子,都要更新父親使他只想自己，而這個關系由孩子維護就好多了，每個孩子只有一個父親，只有設置過的才需要更新，所以顯然，這個父子關系由孩子來維護比較省力.減輕了數據庫的負擔
*現在我們再來看看在沒有 inverse=true 的條件下 ChildPO child = new ChildPO(parent)---〉ChildPO child = new ChildPO()，
代碼: ITxMgr tx = null; tx = HibernateTxMgr.beginTrans("Add a new relationships..."); session = (Session) tx.getS
