Hibernate之HQL基本用法

关于HQL

HQL与SQL非常类似，只不过SQL的操作对象是数据表，列等对象，而HQL操作的是持久化类，实例，属性等。

HQL是完全面向对象的查询语言，因此也具有面向对象的继承，多态等特性。

使用HQL的一般步骤为：

获取session对象

编写HQL语句

使用session的createQuery方法创建查询对象（Query对象）

使用SetXxx(index/para_name, value)为参数复制

使用Query对象的list()方法返回查询结果列表（持久化实体集）

下面演示一下HQL的基本用法，演示之前先附上之前的一个例子，双向N-N关联映射，

假设有下面两个持久化类Person和Event之间成N-N双向关联，代码如下，

Person类

 1 package hql;
 2
 3 import java.util.*;
 4
 5 import javax.persistence.*;
 6
 7
 8 @Entity
 9 @Table(name = "person_inf")
10 public class Person
11 {
12     @Id @Column(name = "person_id")
13     @GeneratedValue(strategy=GenerationType.IDENTITY)
14     private Integer id;
15     private String name;
16     private int age;
17     @ManyToMany(cascade=CascadeType.ALL, targetEntity=MyEvent.class)
18     @JoinTable(name = "person_event" ,
19         joinColumns = @JoinColumn(name = "person_id"
20             , referencedColumnName="person_id"),
21         inverseJoinColumns = @JoinColumn(name = "event_id"
22             , referencedColumnName="event_id")
23     )
24     private Set<MyEvent> myEvents
25         = new HashSet<>();
26     @ElementCollection(targetClass=String.class)
27     @CollectionTable(name="person_email_inf",
28         [email protected](name="person_id" , nullable=false))
29     @Column(name="email_detail" , nullable=false)
30     private Set<String> emails
31         = new HashSet<>();
32
33     public void setId(Integer id)
34     {
35         this.id = id;
36     }
37     public Integer getId()
38     {
39         return this.id;
40     }
41
42     public void setName(String name)
43     {
44         this.name = name;
45     }
46     public String getName()
47     {
48         return this.name;
49     }
50
51     public void setAge(int age)
52     {
53         this.age = age;
54     }
55     public int getAge()
56     {
57         return this.age;
58     }
59
60     public void setMyEvents(Set<MyEvent> myEvents)
61     {
62         this.myEvents = myEvents;
63     }
64     public Set<MyEvent> getMyEvents()
65     {
66         return this.myEvents;
67     }
68
69     public void setEmails(Set<String> emails)
70     {
71         this.emails = emails;
72     }
73     public Set<String> getEmails()
74     {
75         return this.emails;
76     }
77     public Person() {}
78     public Person(String name, int age) {
79         this.name = name;
80         this.age = age;
81     }
82
83 }

Event类

 1 package hql;
 2
 3 import java.util.*;
 4
 5 import javax.persistence.*;
 6
 7 @Entity
 8 @Table(name="event_inf")
 9 public class MyEvent
10 {
11     @Id @Column(name="event_id")
12     @GeneratedValue(strategy=GenerationType.IDENTITY)
13     private Integer id;
14     private String title;
15     private Date happenDate;
16     @ManyToMany(targetEntity=Person.class , mappedBy="myEvents")
17     private Set<Person> actors
18         = new HashSet<>();
19
20     public void setId(Integer id)
21     {
22         this.id = id;
23     }
24     public Integer getId()
25     {
26         return this.id;
27     }
28
29     public void setTitle(String title)
30     {
31         this.title = title;
32     }
33     public String getTitle()
34     {
35         return this.title;
36     }
37
38     public void setHappenDate(Date happenDate)
39     {
40         this.happenDate = happenDate;
41     }
42     public Date getHappenDate()
43     {
44         return this.happenDate;
45     }
46
47     public void setActors(Set<Person> actors)
48     {
49         this.actors = actors;
50     }
51     public Set<Person> getActors()
52     {
53         return this.actors;
54     }
55     public MyEvent() {}
56     public MyEvent(String title, Date happenDate) {
57         this.title = title;
58         this.happenDate = happenDate;
59     }
60 }

PersonManager类

 1 package hql;
 2
 3 import org.hibernate.SessionFactory;
 4 import org.hibernate.Transaction;
 5 import org.hibernate.Session;
 6 import org.hibernate.cfg.Configuration;
 7
 8 import java.text.ParseException;
 9 import java.text.SimpleDateFormat;
10 import java.util.Date;
11 import java.util.Set;
12 import java.util.HashSet;
13
14 public class PersonManager
15 {
16
17     public static void testPerson() throws ParseException
18     {
19         Configuration conf = new Configuration().configure();
20         conf.addAnnotatedClass(Person.class);
21         conf.addAnnotatedClass(MyEvent.class);
22         SessionFactory sf = conf.buildSessionFactory();
23         Session sess = sf.openSession();
24         Transaction tx = sess.beginTransaction();
25         Person p1 = new Person("张三",20);
26         p1.getEmails().add("[email protected]");
27         p1.getEmails().add("[email protected]");
28
29
30         Person p2 = new Person("李四",30);
31         p2.getEmails().add("[email protected]");
32
33
34         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
35         MyEvent e1 = new MyEvent("大学毕业", sdf.parse("2012-06-01"));
36         MyEvent e2 = new MyEvent("参加工作", sdf.parse("2012-10-01"));
37         MyEvent e3 = new MyEvent("出国旅游", sdf.parse("2013-05-01"));
38         MyEvent e4 = new MyEvent("回家过年", sdf.parse("2013-12-20"));
39         MyEvent e5 = new MyEvent("升职加薪", sdf.parse("2014-01-01"));
40
41         p1.getMyEvents().add(e1);
42         p1.getMyEvents().add(e3);
43         p1.getMyEvents().add(e4);
44         p1.getMyEvents().add(e5);
45
46         p2.getMyEvents().add(e2);
47         p2.getMyEvents().add(e3);
48         p2.getMyEvents().add(e4);
49
50         sess.save(p1);
51         sess.save(p2);
52
53         tx.commit();
54         sess.close();
55     }
56
57     public static void main(String[] args) throws ParseException {
58         testPerson();
59     }
60 }

执行上面的