Hibernate一对多数据关联怎么实现
本篇内容主要讲解“Hibernate一对多数据关联怎么实现”，感兴趣的朋友不妨来看看。本文介绍的方法操作简单快捷，实用性强。下面就让小编来带大家学习“Hibernate一对多数据关联怎么实现”吧!
1.数据模型
2.表定义sql
use sample; DROP TABLE T_Address; DROP TABLE T_User; CREATE TABLE T_User ( id INT NOT NULL AUTO_INCREMENT , name VARCHAR(50) , age INT , PRIMARY KEY (id) ); CREATE TABLE T_Address ( id INT NOT NULL AUTO_INCREMENT , address VARCHAR(200) , zipcode VARCHAR(10) , tel VARCHAR(20) , type VARCHAR(20) , user_id INT NOT NULL , idx INT , PRIMARY KEY (id) , INDEX (user_id) , CONSTRAINT FK_T_Address_1 FOREIGN KEY (user_id) REFERENCES T_User (id) );
POJO类
TUser.java
package cn.blogjava.start; import java.util.Set; public class TUser implements java.io.Serializable { // Fields private Integer id; private Integer age; private String name; private Set address; // Constructors public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } public Set getAddress() { return address; } public void setAddress(Set address) { this.address = address; } /** default constructor */ public TUser() { } /** constructor with id */ public TUser(Integer id) { this.id = id; } // Property accessors public Integer getId() { return this.id; } public void setId(Integer id) { this.id = id; } public String getName() { return this.name; } public void setName(String name) { this.name = name; } }
TAddress.java
package cn.blogjava.start; import java.io.Serializable; public class TAddress implements Serializable { private Integer id; private String address; private String zipcode; private String tel; private String type; private Integer userId; private Integer idx; public Integer getId() { return id; } public void setId(Integer id) { this.id = id; } public String getAddress() { return address; } public void setAddress(String address) { this.address = address; } public Integer getIdx() { return idx; } public void setIdx(Integer idx) { this.idx = idx; } public String getTel() { return tel; } public void setTel(String tel) { this.tel = tel; } public String getType() { return type; } public void setType(String type) { this.type = type; } public Integer getUserId() { return userId; } public void setUserId(Integer userId) { this.userId = userId; } public String getZipcode() { return zipcode; } public void setZipcode(String zipcode) { this.zipcode = zipcode; } }
3.配置文件
TUser.hbm.xml
<?xml version="1.0"?> "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="cn.blogjava.start.TUser" table="T_User" catalog="sample" dynamic-update="true" dynamic-insert="true" > <id name="id" type="integer"> <column name="id" /> <generator class="native" /> id> <property name="name" type="string" column="name" /> <property name="age" type="java.lang.Integer" column="age" /> <set name="address" table="t_address" cascade="all" order-by="zipcode asc"> <key column="user_id"> key> <one-to-many class="cn.blogjava.start.TAddress" /> set> class> hibernate-mapping>
TAddress.hbm.xml
注意：没有配置user_id字段。
<?xml version="1.0"?> "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping> <class name="cn.blogjava.start.TAddress" table="T_Address" catalog="sample"> <id name="id" type="integer"> <column name="id" /> <generator class="native" /> id> <property name="address" type="string" column="address" /> <property name="zipcode" type="string" column="zipcode" /> <property name="tel" type="string" column="tel" /> <property name="type" type="string" column="type" /> <property name="idx" type="java.lang.Integer" column="idx" /> class> hibernate-mapping>
4.测试代码
package cn.blogjava.start; import java.util.HashSet; import java.util.Iterator; import java.util.List; import junit.framework.Assert; import junit.framework.TestCase; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; public class HibernateTest extends TestCase { Session session = null; protected void setUp() { try { Configuration config = new Configuration().configure(); SessionFactory sessionFactory = config.buildSessionFactory(); session = sessionFactory.openSession(); } catch (HibernateException e) { e.printStackTrace(); } } protected void tearDown() { try { session.close(); } catch (HibernateException e) { e.printStackTrace(); } } /** * 对象持久化测试(Insert方法) */ public void testInsert() { Transaction tran = null; try { TUser user = new TUser(); user.setName("byf"); user.setAge(new Integer(26)); TAddress addr = new TAddress(); addr.setTel("1123"); addr.setZipcode("233123"); addr.setAddress("HongKong"); TAddress addr2 = new TAddress(); addr2.setTel("139"); addr2.setZipcode("116001"); addr2.setAddress("dalian"); TAddress addr3 = new TAddress(); addr3.setTel("136"); addr3.setZipcode("100080"); addr3.setAddress("beijing"); //设置关联 HashSet set = new HashSet(); set.add(addr); set.add(addr2); set.add(addr3); user.setAddress(set); tran = session.beginTransaction(); //插入user信息 session.save(user); session.flush(); tran.commit(); Assert.assertEquals(user.getId().intValue()>0 ,true); } catch (HibernateException e) { e.printStackTrace(); Assert.fail(e.getMessage()); if(tran != null) { try { tran.rollback(); } catch (Exception e1) { e1.printStackTrace(); } } } } /** * 对象读取测试(Select方法) */ public void testSelect(){ String hql = " from TUser where name='byf'"; try { List userList = session.createQuery(hql).list(); TUser user = (TUser)userList.get(0); System.out.println("user name is " + user.getName()); for (Iterator iter = user.getAddress().iterator(); iter.hasNext();) { TAddress addr = (TAddress) iter.next(); System.out.println("user address is " + addr.getAddress()); } Assert.assertEquals(user.getName(), "byf"); } catch (Exception e) { e.printStackTrace(); Assert.fail(e.getMessage()); } } }
说明:
一个问题，由于是单向关联，为了保持关联关系，我们只能通过主控方对被动方进行级联更新。如果被关联方的字段为NOT NULL属性，当Hibernate一对多创建或者更新关联关系时，可能出现约束违例。
例子中T_Address表中的user_id 为NOT NULL，如果在TAddress.hbm.xml映射了全部字段时。创建一个用户并赋予她地址信息，对于T_Address表而言，Hibernate一对多会执行两条sql语句来保存地址信息。
要执行两条SQL语句，是因为关联是单向的，就是说对于TAddress对象而言，并不知道自己应该与那一个TUser对象关联，只能先将user_id设为一个空值。
之后，根据配置文件
<set name="address" table="t_address" cascade="all" order-by="zipcode asc"> <key column="user_id"> key> <one-to-many class="cn.blogjava.start.TAddress" /> set>
到此，相信大家对“Hibernate一对多数据关联怎么实现”有了更深的了解，不妨来实际操作一番吧！这里是亿速云网站，更多相关内容可以进入相关频道进行查询，关注我们，继续学习！