1. 前言

本章节我们讨论Hibernate一对多查询的处理。

在上一章节中（Hibernate（一）——入门），我们探讨了Hibernate执行最基本的增删改查操作。现在我们将情况复杂化：加入我们在查询用户信息的时候需要同时查询其登录日志，这样就涉及到一对多查询。那么一对多查询要怎么实现么？

2. jar包准备

在本节中，除了上一章节中用到的jar包，我还需要用log4j.jar来将Hibernate的查询语句输出到控制台。log4j.properties的配置如下：

 log4j.rootLogger=info,console

 log4j.appender.console=org.apache.log4j.ConsoleAppender

 log4j.appender.console.layout=org.apache.log4j.PatternLayout

 log4j.appender.console.layout.ConversionPattern=%d %p [%c] - %m%n

log4j的使用方法可查阅：Mybatis之一级缓存（七）中，log4j的学习和使用部分。

3. 数据库准备

我们需要新建立日志表tbLog，并产生部分的测试数据。代码如下：

 CREATE TABLE tbLog (

     logID VARCHAR(50),

     userID VARCHAR(50),

     loginDate DATETIME

 )
 TRUNCATE TABLE tbUser

 TRUNCATE TABLE tbLog

 DECLARE @userID1 VARCHAR(50)

 DECLARE @userID2 VARCHAR(50)

 SET @userID1 = NEWID();

 SET @userID2 = NEWID();

 INSERT INTO tbUser(userID, loginName, userName, passWord)

 SELECT @userID1,'luych','卢艳超','' UNION ALL

 SELECT @userID2,'guest','游客',''

 INSERT INTO tbLog(logID, userID, loginDate)

 SELECT NEWID(), @userID1, '2016-04-01' UNION ALL

 SELECT NEWID(), @userID1, '2016-04-02' UNION ALL

 SELECT NEWID(), @userID1, '2016-04-05' UNION ALL

 SELECT NEWID(), @userID1, '2016-04-08' UNION ALL

 SELECT NEWID(), @userID2, '2016-04-11' UNION ALL

 SELECT NEWID(), @userID2, '2016-04-22'

 SELECT * FROM tbUser;

 SELECT * FROM tbLog;

4. 准备JAVA对象

（1）建立与数据表tbLog相对应的JAVA对象，代码如下：

 package com.luych.hibernate.study.entity;

 import java.util.Date;

 import javax.persistence.Entity;

 import javax.persistence.Id;

 import javax.persistence.Table;

 @Entity

 @Table(name="tbLog")

 public class LogEntity {

     @Id

     private String logID;

     private String userID;

     private Date loginDate;

     public String getLogID() {

         return logID;

     }

     public void setLogID(String logID) {

         this.logID = logID;

     }

     public String getUserID() {

         return userID;

     }

     public void setUserID(String userID) {

         this.userID = userID;

     }

     public Date getLoginDate() {

         return loginDate;

     }

     public void setLoginDate(Date loginDate) {

         this.loginDate = loginDate;

     }

 }

当然，我们同时也要在Hibernate的xml中增加相应的配置

 <mapping class="com.luych.hibernate.study.entity.LogEntity"/>

（2）调整UserEntity对象，建立其与LogEntity的一对多关系。

 package com.luych.hibernate.study.entity;

 import java.text.SimpleDateFormat;

 import java.util.Set;

 import javax.persistence.CascadeType;

 import javax.persistence.Entity;

 import javax.persistence.Id;

 import javax.persistence.JoinColumn;

 import javax.persistence.OneToMany;

 import javax.persistence.Table;

 @Entity

 @Table(name="tbUser")

 public class UserEntity {

     @Id

     private String userID;

     private String loginName;

     private String userName;

     private String passWord;

     @OneToMany(cascade=CascadeType.ALL)

     @JoinColumn(name="userID")

     private Set<LogEntity> logs;

     public String getUserID() {

         return userID;

     }

     public void setUserID(String userID) {

         this.userID = userID;

     }

     public String getLoginName() {

         return loginName;

     }

     public void setLoginName(String loginName) {

         this.loginName = loginName;

     }

     public String getUserName() {

         return userName;

     }

     public void setUserName(String userName) {

         this.userName = userName;

     }

     public String getPassWord() {

         return passWord;

     }

     public void setPassWord(String passWord) {

         this.passWord = passWord;

     }

     public Set<LogEntity> getLogs() {

         return logs;

     }

     public void setLogs(Set<LogEntity> logs) {

         this.logs = logs;

     }

     @Override

     public String toString() {

         String str = loginName+", "+userName+", "+passWord+", "+userID+" 登录日志：\n";

         for (LogEntity log: logs) {

             str = str+new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(log.getLoginDate())+"\n";

         }

         return str;

     }

 }

其中，

    • @OneToMany的cascade可取值为：

      CascadeType.PERSIST：级联新建，本例中即生成User的时候同时生成Log。
      CascadeType.REMOVE : 级联删除，本例中即删除User的时候同时删除Log。
      CascadeType.REFRESH：级联刷新，本例中即查询User的时候同时查询Log。
      CascadeType.MERGE  ：级联更新，本例中即修改User的时候同时修改Log。
      CascadeType.ALL    ：以上全部四项，即上面四个全都执行。
    • @JoinColumn的name取值为：LogEntity中的userID属性。

5. 调整Hibernate配置文件

 <?xml version="1.0" encoding="UTF-8"?>

 <!DOCTYPE hibernate-configuration PUBLIC

         "-//Hibernate/Hibernate Configuration DTD 5.0//EN"

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

 <hibernate-configuration>

     <session-factory>

         <!-- 设置数据库驱动 -->

         <property name="hibernate.connection.driver_class">com.microsoft.sqlserver.jdbc.SQLServerDriver</property>

         <!-- 设置数据库URL -->

         <property name="hibernate.connection.url">jdbc:sqlserver://192.168.9.23:14433;databaseName=tempdb</property>

         <!-- 数据库用户名 -->

         <property name="hibernate.connection.username">sa</property>

         <!-- 数据库密码 -->

         <property name="hibernate.connection.password">123@abcd</property>

         <!-- 打印sql -->

         <property name="show_sql">true</property>

         <property name="format_sql">false</property>

         <!-- beans -->

         <mapping class="com.luych.hibernate.study.entity.UserEntity"/>

         <mapping class="com.luych.hibernate.study.entity.LogEntity"/>

     </session-factory>

 </hibernate-configuration>

我们增加了针对show_sql和format_sql的配置，加上这两个配置后，Hibernate会输出执行的SQL脚本。

    • show_sql：true，输出SQL脚本。false，不输出。
    • format_sql：true，格式化SQL脚本。false，不格式化。

本例中，并没有将format_sql设置为true，是因为格式化的SQL在控制台中显示很占篇幅，不利于我们后面看测试结果，所以关闭了。

6. 测试运行结果

 package com.luych.hibernate.study.main;

 import java.util.Date;

 import java.util.HashSet;

 import java.util.List;

 import java.util.Set;

 import java.util.UUID;

 import org.hibernate.Query;

 import org.hibernate.Session;

 import org.hibernate.SessionFactory;

 import org.hibernate.cfg.Configuration;

 import org.junit.After;

 import org.junit.Before;

 import org.junit.Test;

 import com.luych.hibernate.study.entity.LogEntity;

 import com.luych.hibernate.study.entity.UserEntity;

 @SuppressWarnings("unchecked")

 public class TestMain {

     private Session session;

     @Before

     public void getSession(){

         Configuration config = new Configuration().configure("hibernate-config.xml");

         SessionFactory sessionFactory = config.buildSessionFactory();

         session = sessionFactory.openSession();

     }

     @After

     public void freeSession(){

         session.close();

     }

     public void sel() {

         Query query = session.createQuery("FROM UserEntity WHERE 1=1");

         List<UserEntity> userList = query.list();

         for (UserEntity userEntity : userList) {

             System.out.println(userEntity.toString());

         }

     }

     public void add() {

         session.beginTransaction();

         String userID = UUID.randomUUID().toString();

         UserEntity user  = new UserEntity();

         user.setLoginName("admin");

         user.setUserName("系统管理员");

         user.setPassWord("");

         user.setUserID(userID);

         LogEntity log1 = new LogEntity();

         log1.setLogID(UUID.randomUUID().toString());

         log1.setUserID(userID);

         log1.setLoginDate(new Date());

         LogEntity log2 = new LogEntity();

         log2.setLogID(UUID.randomUUID().toString());

         log2.setUserID(userID);

         log2.setLoginDate(new Date());

         Set<LogEntity> logs = new HashSet<LogEntity>();

         logs.add(log1);

         logs.add(log2);

         user.setLogs(logs);

         session.save(user);

         session.getTransaction().commit();

     }

     public void edt(){

         session.beginTransaction();

         Query query = session.createQuery("FROM UserEntity WHERE 1=1");

         List<UserEntity> userList = query.list();

         for (UserEntity userEntity : userList) {

             userEntity.setPassWord("");

             LogEntity log = new LogEntity();

             log.setLogID(UUID.randomUUID().toString());

             log.setUserID(userEntity.getUserID());

             log.setLoginDate(new Date());

             userEntity.getLogs().add(log);

             session.update(userEntity);

         }

         session.getTransaction().commit();

     }

     public void del(){

         session.beginTransaction();

         Query query = session.createQuery("FROM UserEntity WHERE 1=1");

         List<UserEntity> userList = query.list();

         for (UserEntity userEntity : userList) {

             session.delete(userEntity);

         }

         session.getTransaction().commit();

     }

     @Test

     public void test(){

         System.out.println("\n----------现有用户：");

         sel();

         System.out.println("\n----------开始增加用户：");

         add();

         System.out.println("\n----------增加用户后：");

         sel();

         System.out.println("\n----------开始修改用户：");

         edt();

         System.out.println("\n----------修改用户后：");

         sel();

         System.out.println("\n----------开始删除用户：");

         del();

         System.out.println("\n----------删除用户后：");

         sel();

     }

 }

getSession和freeSession和上一章节中相同，不再赘述。

add方法，新建了一个用户并设定了两条登录日志，然后保存。edt方法，将所有用户的密码改为45666，并为所有的用户增加一条登录日志。del方法，删除所有的用户。sel方法，查询所有用户信息并输出到控制台。

右键，Run As JUnit Test后，控制台输出结果为：

 ----------现有用户：

 Hibernate: select userentity0_.userID as userID1_1_, userentity0_.loginName as loginNam2_1_, 
                      userentity0_.passWord as passWord3_1_, userentity0_.userName as userName4_1_ 
               from tbUser userentity0_ where 1=1

 Hibernate: select logs0_.userID as userID3_0_0_, logs0_.logID as logID1_0_0_, 
                      logs0_.logID as logID1_0_1_, logs0_.loginDate as loginDat2_0_1_, logs0_.userID as userID3_0_1_ 
               from tbLog logs0_ where logs0_.userID=?

 luych, 卢艳超, 12333, CB6172E3-8750-4718-BEF6-EE0917015FA9 登录日志：

 2016-04-01 00:00:00

 2016-04-08 00:00:00

 2016-04-05 00:00:00

 2016-04-02 00:00:00

 Hibernate: select logs0_.userID as userID3_0_0_, logs0_.logID as logID1_0_0_, 
                      logs0_.logID as logID1_0_1_, logs0_.loginDate as loginDat2_0_1_, logs0_.userID as userID3_0_1_ 
               from tbLog logs0_ where logs0_.userID=?

 guest, 游客, 12333, 21539577-A3D1-4A1F-8D10-6ED0540A46A0 登录日志：

 2016-04-11 00:00:00

 2016-04-22 00:00:00

 ----------开始增加用户：

 Hibernate: select logentity_.logID, logentity_.loginDate as loginDat2_0_, logentity_.userID as userID3_0_ 
               from tbLog logentity_ where logentity_.logID=?

 Hibernate: select logentity_.logID, logentity_.loginDate as loginDat2_0_, logentity_.userID as userID3_0_ 
               from tbLog logentity_ where logentity_.logID=?

 Hibernate: insert into tbUser (loginName, passWord, userName, userID) values (?, ?, ?, ?)

 Hibernate: insert into tbLog (loginDate, userID, logID) values (?, ?, ?)

 Hibernate: insert into tbLog (loginDate, userID, logID) values (?, ?, ?)

 Hibernate: update tbLog set userID=? where logID=?

 Hibernate: update tbLog set userID=? where logID=?

 ----------增加用户后：

 Hibernate: select userentity0_.userID as userID1_1_, userentity0_.loginName as loginNam2_1_, 
                      userentity0_.passWord as passWord3_1_, userentity0_.userName as userName4_1_ 
               from tbUser userentity0_ where 1=1

 luych, 卢艳超, 12333, CB6172E3-8750-4718-BEF6-EE0917015FA9 登录日志：

 2016-04-01 00:00:00

 2016-04-08 00:00:00

 2016-04-05 00:00:00

 2016-04-02 00:00:00

 guest, 游客, 12333, 21539577-A3D1-4A1F-8D10-6ED0540A46A0 登录日志：

 2016-04-11 00:00:00

 2016-04-22 00:00:00

 admin, 系统管理员, 12333, 99d5d264-9d02-4e45-a8c5-f710cc14107e 登录日志：

 2016-04-26 17:06:00

 2016-04-26 17:06:00

 ----------开始修改用户：

 Hibernate: select userentity0_.userID as userID1_1_, userentity0_.loginName as loginNam2_1_, 
                      userentity0_.passWord as passWord3_1_, userentity0_.userName as userName4_1_ 
               from tbUser userentity0_ where 1=1

 Hibernate: select logentity_.logID, logentity_.loginDate as loginDat2_0_, 
                      logentity_.userID as userID3_0_ 
               from tbLog logentity_ where logentity_.logID=?

 Hibernate: select logentity_.logID, logentity_.loginDate as loginDat2_0_, 
                      logentity_.userID as userID3_0_ 
               from tbLog logentity_ where logentity_.logID=?

 Hibernate: select logentity_.logID, logentity_.loginDate as loginDat2_0_, 
                      logentity_.userID as userID3_0_ 
               from tbLog logentity_ where logentity_.logID=?

 Hibernate: insert into tbLog (loginDate, userID, logID) values (?, ?, ?)

 Hibernate: insert into tbLog (loginDate, userID, logID) values (?, ?, ?)

 Hibernate: insert into tbLog (loginDate, userID, logID) values (?, ?, ?)

 Hibernate: update tbUser set loginName=?, passWord=?, userName=? where userID=?

 Hibernate: update tbUser set loginName=?, passWord=?, userName=? where userID=?

 Hibernate: update tbUser set loginName=?, passWord=?, userName=? where userID=?

 Hibernate: update tbLog set userID=? where logID=?

 Hibernate: update tbLog set userID=? where logID=?

 Hibernate: update tbLog set userID=? where logID=?

 ----------修改用户后：

 Hibernate: select userentity0_.userID as userID1_1_, userentity0_.loginName as loginNam2_1_, 
                      userentity0_.passWord as passWord3_1_, userentity0_.userName as userName4_1_ 
               from tbUser userentity0_ where 1=1

 luych, 卢艳超, 45666, CB6172E3-8750-4718-BEF6-EE0917015FA9 登录日志：

 2016-04-01 00:00:00

 2016-04-08 00:00:00

 2016-04-05 00:00:00

 2016-04-02 00:00:00

 2016-04-26 17:06:00

 guest, 游客, 45666, 21539577-A3D1-4A1F-8D10-6ED0540A46A0 登录日志：

 2016-04-11 00:00:00

 2016-04-22 00:00:00

 2016-04-26 17:06:00

 admin, 系统管理员, 45666, 99d5d264-9d02-4e45-a8c5-f710cc14107e 登录日志：

 2016-04-26 17:06:00

 2016-04-26 17:06:00

 2016-04-26 17:06:00

 ----------开始删除用户：

 Hibernate: select userentity0_.userID as userID1_1_, userentity0_.loginName as loginNam2_1_, 
                      userentity0_.passWord as passWord3_1_, userentity0_.userName as userName4_1_ 
               from tbUser userentity0_ where 1=1

 Hibernate: update tbLog set userID=null where userID=?

 Hibernate: update tbLog set userID=null where userID=?

 Hibernate: update tbLog set userID=null where userID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbUser where userID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbUser where userID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbLog where logID=?

 Hibernate: delete from tbUser where userID=?

 ----------删除用户后：

 Hibernate: select userentity0_.userID as userID1_1_, userentity0_.loginName as loginNam2_1_, 
                      userentity0_.passWord as passWord3_1_, userentity0_.userName as userName4_1_ 
               from tbUser userentity0_ where 1=1

从打印结果中，我们可以看到，新增、编辑、删除用户信息的时候，Hibernate都帮我们完成登录日志的新增、删除、操作。查询的时候也如此。

但是需要提点的是：在Hibernate第一次查询中，我们看到它先查询了tbUser表，然后针对tbUser表的每一个记录都又查询了下tbLog表，这就是经典的N+1查询问题，所以效率嘛…

以上就是Hibernate中一对多的查询关联，其他关联情况将在后续的博文中讲解。

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