学步园

Hibernate对持久化类的操作非常方便，而级联操作也是功能强大。但是级联操作会带来莫名其妙的问题，下面就提出一个非常微妙的问题，即

hbm文件中定义的集合Set在顺序不同的情况下，对操作会带来不同的影响。下面用一个例子来说明一下该问题。

持久化类描述：

//M，最外层的类，两个集合<br /> public class M {<br /> private Integer id;<br /> private Set<I> is;<br /> private Set<S> ss;<br /> }<br /> //I，只引用了M<br /> public class I {<br /> private Integer id;<br /> private M M;<br /> }<br /> //S，引用了I和M<br /> public class S {<br /> private Integer id;<br /> private M M;<br /> private I I;<br /> }

M.hbm.xml:

<hibernate-mapping><br /> <class name="M" table="mm" catalog="cascade"><br /> <id name="id" type="java.lang.Integer"><br /> <column name="id" /><br /> <generator class="native" /><br /> </id><br /> <set name="is" inverse="true" cascade="all"><br /> <key><br /> <column name="mid" not-null="true" /><br /> </key><br /> <one-to-many class="I" /><br /> </set><br /> <set name="ss" inverse="true" cascade="all"><br /> <key><br /> <column name="mid" not-null="true" /><br /> </key><br /> <one-to-many class="S" /><br /> </set><br /> </class><br /> </hibernate-mapping><br />

操作测试：

public class Test {<br /> public static void main(String[] args) {<br /> save();<br /> // delete();<br /> }</p> <p> public static void save(){<br /> M m = new M();<br /> I i = new I();<br /> S s = new S();</p> <p> i.setM(m);</p> <p> s.setM(m);<br /> s.setI(i);</p> <p> Set<I> is = new HashSet<I>();<br /> is.add(i);<br /> Set<S> ss = new HashSet<S>();<br /> ss.add(s);</p> <p> m.setSs(ss);<br /> m.setIs(is);</p> <p> Configuration cfg = new Configuration();<br /> cfg.configure();<br /> SessionFactory fac = cfg.buildSessionFactory();</p> <p> Session sess = fac.openSession();<br /> Transaction tx = sess.beginTransaction();<br /> sess.save(m);<br /> tx.commit();<br /> sess.close();<br /> }</p> <p> public static void delete(){<br /> Configuration cfg = new Configuration();<br /> cfg.configure();<br /> SessionFactory fac = cfg.buildSessionFactory();</p> <p> Session sess = fac.openSession();<br /> Transaction tx = sess.beginTransaction();<br /> M m = (M)sess.get(M.class, 1);<br /> sess.delete(m);<br /> tx.commit();<br /> sess.close();<br /> }<br /> }<br />

操作结果正常：

Hibernate: insert into cascade.mm values ( )<br /> Hibernate: insert into cascade.ii (mid) values (?)<br /> Hibernate: insert into cascade.ss (iid, mid) values (?, ?)

但是删除不正常：

Hibernate: select m0_.id as id1_0_ from cascade.mm m0_ where m0_.id=?<br /> Hibernate: select is0_.mid as mid1_1_, is0_.id as id1_, is0_.id as id0_0_, is0_.mid as mid0_0_ from cascade.ii is0_ where is0_.mid=?<br /> Hibernate: select ss0_.mid as mid1_1_, ss0_.id as id1_, ss0_.id as id2_0_, ss0_.iid as iid2_0_, ss0_.mid as mid2_0_ from cascade.ss ss0_ where ss0_.mid=?<br /> Exception in thread "main" org.hibernate.PropertyValueException: not-null property references a null or transient value: S.I<br /> at org.hibernate.engine.Nullability.checkNullability(Nullability.java:101)<br /> at org.hibernate.event.def.DefaultDeleteEventListener.deleteEntity(DefaultDeleteEventListener.java:272)<br /> at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:163)<br /> at org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:957)<br /> at org.hibernate.impl.SessionImpl.delete(SessionImpl.java:940)<br /> at org.hibernate.engine.CascadingAction$1.cascade(CascadingAction.java:145)<br /> at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:392)<br /> at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:335)<br /> at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204)<br /> at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:425)<br /> at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:362)<br /> at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:338)<br /> at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204)<br /> at org.hibernate.engine.Cascade.cascade(Cascade.java:161)<br /> at org.hibernate.event.def.DefaultDeleteEventListener.cascadeBeforeDelete(DefaultDeleteEventListener.java:329)<br /> at org.hibernate.event.def.DefaultDeleteEventListener.deleteEntity(DefaultDeleteEventListener.java:268)<br /> at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:163)<br /> at org.hibernate.event.def.DefaultDeleteEventListener.onDelete(DefaultDeleteEventListener.java:74)<br /> at org.hibernate.impl.SessionImpl.fireDelete(SessionImpl.java:948)<br /> at org.hibernate.impl.SessionImpl.delete(SessionImpl.java:926)<br /> at Test.delete(Test.java:55)<br /> at Test.main(Test.java:15) 

修改M.hbm.xml为：

<hibernate-mapping><br /> <class name="M" table="mm" catalog="cascade"><br /> <id name="id" type="java.lang.Integer"><br /> <column name="id" /><br /> <generator class="native" /><br /> </id><br /> <set name="ss" inverse="true" cascade="all"><br /> <key><br /> <column name="mid" not-null="true" /><br /> </key><br /> <one-to-many class="S" /><br /> </set><br /> <set name="is" inverse="true" cascade="all"><br /> <key><br /> <column name="mid" not-null="true" /><br /> </key><br /> <one-to-many class="I" /><br /> </set><br /> </class><br /> </hibernate-mapping><br />

则删除正常：

Hibernate: select m0_.id as id1_0_ from cascade.mm m0_ where m0_.id=?<br /> Hibernate: select ss0_.mid as mid1_1_, ss0_.id as id1_, ss0_.id as id2_0_, ss0_.iid as iid2_0_, ss0_.mid as mid2_0_ from cascade.ss ss0_ where ss0_.mid=?<br /> Hibernate: select is0_.mid as mid1_1_, is0_.id as id1_, is0_.id as id0_0_, is0_.mid as mid0_0_ from cascade.ii is0_ where is0_.mid=?<br /> Hibernate: delete from cascade.ss where id=?<br /> Hibernate: delete from cascade.ii where id=?<br /> Hibernate: delete from cascade.mm where id=?<br />

但是插入又不正常了：

Hibernate: insert into cascade.mm values ( )<br /> Exception in thread "main" org.hibernate.PropertyValueException: not-null property references a null or transient value: S.I<br /> at org.hibernate.engine.Nullability.checkNullability(Nullability.java:101)<br /> at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:313)<br /> at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)<br /> at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.performSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:117)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)<br /> at org.hibernate.impl.SessionImpl.fireSaveOrUpdate(SessionImpl.java:677)<br /> at org.hibernate.impl.SessionImpl.saveOrUpdate(SessionImpl.java:669)<br /> at org.hibernate.engine.CascadingAction$5.cascade(CascadingAction.java:252)<br /> at org.hibernate.engine.Cascade.cascadeToOne(Cascade.java:392)<br /> at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:335)<br /> at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204)<br /> at org.hibernate.engine.Cascade.cascadeCollectionElements(Cascade.java:425)<br /> at org.hibernate.engine.Cascade.cascadeCollection(Cascade.java:362)<br /> at org.hibernate.engine.Cascade.cascadeAssociation(Cascade.java:338)<br /> at org.hibernate.engine.Cascade.cascadeProperty(Cascade.java:204)<br /> at org.hibernate.engine.Cascade.cascade(Cascade.java:161)<br /> at org.hibernate.event.def.AbstractSaveEventListener.cascadeAfterSave(AbstractSaveEventListener.java:476)<br /> at org.hibernate.event.def.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:354)<br /> at org.hibernate.event.def.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:204)<br /> at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:130)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGeneratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:210)<br /> at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrRequestedId(DefaultSaveEventListener.java:56)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTransient(DefaultSaveOrUpdateEventListener.java:195)<br /> at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(DefaultSaveEventListener.java:50)<br /> at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpdate(DefaultSaveOrUpdateEventListener.java:93)<br /> at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:705)<br /> at org.hibernate.impl.SessionImpl.save(SessionImpl.java:693)<br /> at org.hibernate.impl.SessionImpl.save(SessionImpl.java:689)<br /> at Test.save(Test.java:42)<br /> at Test.main(Test.java:14)<br />

问题处在何方？为何跟M.hbm.xml里面的set顺序有关系呢？如何统一解决呢？