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

 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">                                                  id>                                                      key>                      set>     class> hibernate-mapping>

TAddress.hbm.xml
注意：没有配置user_id字段。

 "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">                                                  id>                                                  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

                          key>                      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！