HQL实现多对多关联查询（无关系表的映射）

HQL实现多对多关联查询（无关系表的映射）

目录：

1. 应用场景
2. 演示

[一]、应用场景

在用注解的方式（@ManyToMany @JoinTable）实现多对多映射时，并没有具体的多对多关系表的实体类，那么我们如何利用HQL实现关联查询呢？比如：学生和课程表之间的多对多关系。

[二]、演示

1.实体类

IdEntity.java

1 package com.micmiu.hibernate.anno.entity;
2
3 import javax.persistence.Column;
4 import javax.persistence.GeneratedValue;
5 import javax.persistence.Id;
6 import javax.persistence.MappedSuperclass;
7
8 /**
9  * 统一定义id的entity基类.
10  *
11  * 基类统一定义id的属性名称、数据类型、列名映射及生成策略.
12  * 子类可重载getId()函数重定义id的列名映射和生成策略.
13  *
14  * @author Michael Sun
15  */
16 @MappedSuperclass
17 public abstract class IdEntity {
18
19     protected Long id;
20
21     @Id
22     @Column(name = "ID")
23     @GeneratedValue
24     // @GeneratedValue(strategy = GenerationType.SEQUENCE)
25     // @GeneratedValue(generator = "system-uuid")
26     // @GenericGenerator(name = "system-uuid", strategy = "uuid")
27     public Long getId() {
28         return id;
29     }
30
31     public void setId(Long id) {
32         this.id = id;
33     }
34 }

学生实体类：Student.java

1 package com.micmiu.hibernate.anno.entity;
2
3 import java.util.Collection;
4 import java.util.Date;
5
6 import javax.persistence.Column;
7 import javax.persistence.Entity;
8 import javax.persistence.JoinColumn;
9 import javax.persistence.JoinTable;
10 import javax.persistence.ManyToMany;
11 import javax.persistence.OrderBy;
12 import javax.persistence.Table;
13
14 import org.hibernate.annotations.Fetch;
15 import org.hibernate.annotations.FetchMode;
16
17 /**
18  *
19  * Description:
20  *
21  * @author Michael
22  * @see http://www.micmiu.com
23  * @time Create on 2013-6-6 下午2:40:08
24  * @version 1.0
25  */
26 @Entity
27 @Table(name = "DEMO_T_STUDENT")
28 public class Student extends IdEntity {
29
30     @Column(name = "NAME")
31     private String name;
32
33     @Column(name = "BIRTHDAY")
34     private Date birthday;
35
36     private Collection courses;
37
38     public String getName() {
39         return name;
40     }
41
42     public void setName(String name) {
43         this.name = name;
44     }
45
46     public Date getBirthday() {
47         return birthday;
48     }
49
50     public void setBirthday(Date birthday) {
51         this.birthday = birthday;
52     }
53
54     @ManyToMany
55     @JoinTable(name = "DEMO_R_S2C", joinColumns = { @JoinColumn(name = "SID") }, inverseJoinColumns = { @JoinColumn(name = "CID") })
56     @Fetch(FetchMode.SUBSELECT)
57     @OrderBy("id")
58     public Collection getCourses() {
59         return courses;
60     }
61
62     public void setCourses(Collection courses) {
63         this.courses = courses;
64     }
65
66     @Override
67     public String toString() {
68         return "Student [name=" + name + ", birthday=" + birthday + "]";
69     }
70
71 }

课程实体类：Course.java

1 package com.micmiu.hibernate.anno.entity;
2
3 import javax.persistence.Column;
4 import javax.persistence.Entity;
5 import javax.persistence.Table;
6
7 /**
8  *
9  * Description:
10  *
11  * @author Michael
12  * @see http://www.micmiu.com
13  * @time Create on 2013-6-6 下午2:52:31
14  * @version 1.0
15  */
16 @Entity
17 @Table(name = "DEMO_T_COURSE")
18 public class Course extends IdEntity {
19
20     @Column(name = "NAME")
21     private String name;
22
23     public String getName() {
24         return name;
25     }
26
27     public void setName(String name) {
28         this.name = name;
29     }
30
31     @Override
32     public String toString() {
33         return "Course [name=" + name + "]";
34     }
35
36 }

2.初始化数据：

利用dbunit初始化演示数据：

1 xml version='1.0' encoding="utf-8"?>
2 <dataset>
3     <demo_t_student id="101" name="micmiu.com" birthday="2012-12-12" />
4     <demo_t_student id="102" name="[email protected]" birthday="2008-08-08" />
5     <demo_t_student id="103" name="ctosun.com" birthday="2013-01-04" />
6
7     <demo_t_course id="901" name="chinese" />
8     <demo_t_course id="902" name="english" />
9     <demo_t_course id="903" name="math" />
10
11     <demo_r_s2c sid="101" cid="901" />
12     <demo_r_s2c sid="101" cid="902" />
13     <demo_r_s2c sid="101" cid="903" />
14     <demo_r_s2c sid="102" cid="902" />
15     <demo_r_s2c sid="102" cid="903" />
16     <demo_r_s2c sid="103" cid="903" />
17
18 dataset>

3.演示关联查询

在Student中配置了多对多关系，在Course没有配置多对多关系，下面将分别演示关联查询这两个实体的方法：

测试基础类 HibernateBaseTest.java

1 package com.micmiu.hibernate;
2
3 import org.hibernate.SessionFactory;
4 import org.hibernate.cfg.Configuration;
5 import org.hibernate.service.ServiceRegistry;
6 import org.hibernate.service.ServiceRegistryBuilder;
7 import org.junit.AfterClass;
8 import org.junit.BeforeClass;
9 import org.junit.Test;
10
11 /**
12  *
13  * Description:
14  *
15  * @author Michael
16  * @see http://www.micmiu.com
17  * @time Create on 2013-6-6 下午7:31:02
18  * @version 1.0
19  */
20 public abstract class HibernateBaseTest {
21
22     protected static SessionFactory sessionFactory;
23
24     @BeforeClass
25     public static void beforeClass() {
26         Configuration configuration = new Configuration().configure();
27         ServiceRegistry serviceRegistry = new ServiceRegistryBuilder()
28                 .applySettings(configuration.getProperties())
29                 .buildServiceRegistry();
30         sessionFactory = configuration.buildSessionFactory(serviceRegistry);
31
32     }
33
34     @AfterClass
35     public static void afterClass() {
36         sessionFactory.close();
37     }
38
39     @Test
40     public abstract void testMethod();
41
42 }

测试HQL查询：ManyToManyTest.java

1 package com.micmiu.hibernate;
2
3 import java.util.List;
4
5 import org.hibernate.Query;
6 import org.hibernate.Session;
7 import org.junit.Assert;
8 import org.junit.Test;
9
10 import com.micmiu.hibernate.anno.entity.Course;
11 import com.micmiu.hibernate.anno.entity.Student;
12
13 /**
14  *
15  * Description:测试 注解配置多对多关系的表之间的联合查询
16  *
17  * @author Michael
18  * @see http://www.micmiu.com
19  * @time Create on 2013-6-7 上午11:38:49
20  * @version 1.0
21  */
22 public class ManyToManyTest extends HibernateBaseTest {
23
24     @Override
25     @Test
26     public void testMethod() {
27         // 测试查询有配置多对多关系的对象
28         test1();
29         // 测试查询无配置多对多关系的对象
30         test2();
31
32     }
33
34     /**
35      * 测试查询有配置多对多关系的对象
36      */
37     @SuppressWarnings("unchecked")
38     public void test1() {
39         Session session = sessionFactory.openSession();
40
41         session.beginTransaction();
42         String hql = "select s from Student s join s.courses c where s.name like '%micmiu.com%' and c.name ='math'";
43         String hql2 = "select s from Student s,Course c where c.id in elements (s.courses) and s.name like '%micmiu.com%' and c.name ='math'";
44         Query query = session.createQuery(hql);
45
46         List list = query.list();
47         System.out.println("----------- size:" + list.size());
48         Assert.assertEquals(1, list.size());
49
50         for (Student s : list) {
51             Assert.assertEquals("micmiu.com", s.getName());
52             System.out.println(s);
53         }
54
55         session.getTransaction().commit();
56         session.close();
57     }
58
59     /**
60      * 测试查询无配置多对多关系的对象
61      */
62     @SuppressWarnings("unchecked")
63     public void test2() {
64         Session session = sessionFactory.openSession();
65
66         session.beginTransaction();
67         String hql = "select distinct c from Student s,Course c where c.id in elements (s.courses) and s.name like '%micmiu.com%' and c.name ='math'";
68
69         Query query = session.createQuery(hql);
70
71         List list = query.list();
72         System.out.println("----------- size:" + list.size());
73         Assert.assertEquals(1, list.size());
74         for (Course c : list) {
75             Assert.assertEquals("math", c.getName());
76             System.out.println(c);
77         }
78
79         session.getTransaction().commit();
80         session.close();
81     }
82 }

执行结果：单元测试通过，运行日志如下：

Hibernate:

select

student0_.ID as ID1_,

student0_.birthday as birthday1_,

student0_.name as name1_

from

DEMO_T_STUDENT student0_

inner join

DEMO_R_S2C courses1_

on student0_.ID=courses1_.SID

inner join

DEMO_T_COURSE course2_

on courses1_.CID=course2_.ID

where

(

student0_.name like ‘%micmiu.com%’

)

and course2_.name=’math’

———– size:1

Student [name=micmiu.com, birthday=2012-12-12 00:00:00.0]

Hibernate:

select

distinct course1_.ID as ID0_,

course1_.name as name0_

from

DEMO_T_STUDENT student0_ cross

join

DEMO_T_COURSE course1_

where

(

course1_.ID in (

select

courses2_.CID

from

DEMO_R_S2C courses2_

where

student0_.ID=courses2_.SID

)

)

and (

student0_.name like ‘%micmiu.com%’

)

and course1_.name=’math’

———– size:1

Course [name=math]