hibernate 多对多
Category Item
类别 商品
单向多对多。
package com.hibernate.n2n; import java.util.HashSet; import java.util.Set; public class Category { private Integer cid; private String cname; private Set<Item> items=new HashSet<Item>(); public Integer getCid() { return cid; } public void setCid(Integer cid) { this.cid = cid; } public String getCname() { return cname; } public void setCname(String cname) { this.cname = cname; } public Set<Item> getItems() { return items; } public void setItems(Set<Item> items) { this.items = items; } }
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.hibernate.n2n"> <class name="Category" table="categories"> <id name="cid" type="java.lang.Integer"> <column name="c_id" /> <!-- 指定主键的生成方式, native: 使用数据库本地方式 --> <generator class="native" /> </id> <property name="cname" type="java.lang.String" column="c_name" > </property> <!-- name 对应items的属性名。 table 是一个中间表--> <set name="items" table="Category_Items"> <key column="c_id"></key> 设置category在中间表的外键 <many-to-many class="Item" column="i_id" ></many-to-many> 设置item在中间表的外键。 </set> </class> </hibernate-mapping>
package com.hibernate.n2n; public class Item { private Integer iid; private String iname; public Integer getIid() { return iid; } public void setIid(Integer iid) { this.iid = iid; } public String getIname() { return iname; } public void setIname(String iname) { this.iname = iname; } }
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping package="com.hibernate.n2n"> <class name="Item" table="item" > <id name="iid" type="java.lang.Integer"> <column name="i_id" /> <!-- 指定主键的生成方式, native: 使用数据库本地方式 --> <generator class="native" /> </id> <property name="iname" type="java.lang.String" column="i_name" > </property> </class> </hibernate-mapping>
测试添加：
@org.junit.Test public void testSave(){ Category category1=new Category(); category1.setCname("CA1"); Category category2=new Category(); category2.setCname("CA1"); Item item1=new Item(); item1.setIname("IA1"); Item item2=new Item(); item2.setIname("IA2"); //维护关系. category1.getItems().add(item1); category1.getItems().add(item2); category2.getItems().add(item1); category2.getItems().add(item2); session.save(category1); session.save(category2); session.save(item1); session.save(item2); }
也是支持懒加载的。
查询item的时候。是查询的中间表。
双向N---N
只是在对象中加上set集合。
配置文件加上：set
1 <set name="categorys" table="Category_Items"> 在item对象中的category属性。 2 <key column="i_id"></key> item在中间表中的外键 3 <many-to-many class="Category" column="c_id" ></many-to-many> category在中间表中的外键。 4 </set>
执行保存的时候会出现错误。 这是因为双方都维护了关系。导致主键发生冲突。
解决方案：在其中一个set 加上 inverse="true"
org.hibernate.exception.ConstraintViolationException: could not execute statement at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:74) at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49) at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125) at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110) at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:136) at org.hibernate.engine.jdbc.batch.internal.NonBatchingBatch.addToBatch(NonBatchingBatch.java:58) at org.hibernate.persister.collection.AbstractCollectionPersister.recreate(AbstractCollectionPersister.java:1256) at org.hibernate.action.internal.CollectionRecreateAction.execute(CollectionRecreateAction.java:58) at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:377) at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:369) at org.hibernate.engine.spi.ActionQueue.executeActions(ActionQueue.java:292) at org.hibernate.event.internal.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:339) at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:52) at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1234) at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:404) at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101) at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175) at com.hibernate.n2n.Test.destroy(Test.java:34) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44) at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15) at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41) at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:37) at org.junit.runners.BlockJUnit4ClassRunner.runNotIgnored(BlockJUnit4ClassRunner.java:79) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:71) at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:49) at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193) at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52) at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191) at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42) at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184) at org.junit.runners.ParentRunner.run(ParentRunner.java:236) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197) Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '8-5' for key 'PRIMARY' at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39) at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27) at java.lang.reflect.Constructor.newInstance(Constructor.java:513) at com.mysql.jdbc.Util.handleNewInstance(Util.java:406) at com.mysql.jdbc.Util.getInstance(Util.java:381) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1015) at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:956) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3515) at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3447) at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1951) at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2101) at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2554) at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:1761) at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2046) at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1964) at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:1949) at com.mchange.v2.c3p0.impl.NewProxyPreparedStatement.executeUpdate(NewProxyPreparedStatement.java:147) at org.hibernate.engine.jdbc.internal.ResultSetReturnImpl.executeUpdate(ResultSetReturnImpl.java:133) ... 36 more
