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JPA入门�Q?

天独 — Thu, 22 Apr 2010 12:01:00 GMT

有半个月没有更新了，倒不是我没有�l�箋学习�Q�工作比较忙�Q�晚上学习的旉��短，没有太多旉��写blog
今天�Q�说CallBack�Q�JPA为我们提供了一些在�q�行CURD前后的一些callback methods�Q�这些方法可以在我们�q�行数据持久化和查询前后�Q�进行一些操作，比如�U�录日志�?br /> 先来介绍写有几种callback methods annotation�Q?br /> @PerPresist 持久化之前调用调�?br /> @PostPersist 持久化之后（官方文档是在Object状态变�?Persist 状态）
@PostLoad 查询之后
@PreUpdate和@PostUpdate �q�两个分别是在更��C��前和之后�Q�不�q�这两个必须是在PostLoad之后�Q�对查询出来的数据进行更斎ͼ�才会触发
@PreRemove和@PostReomve 分别是删除前和删除后�Q�官�Ҏ��档是Object状态变为deleted 状态）

下面是我的例子，当然�q�里只有关键代码�Q?br /> 2010�q?�?2�?星期�?br />

1 @PrePersist
2     public void logPrePersist() {
3         logger.info("PrePersist " + this.getTitle());
4     }
5
6     @PostPersist
7     public void logPostPersist() {
8         logger.info("PostPersist " + this.getTitle());
9     }
10
11     @PostLoad
12     public void logPostLoad() {
13         logger.info("PostLoad " + this.getTitle());
14     }
15
16     @PreUpdate
17     public void logPreUpdate() {
18         logger.info("PreUpdate " + this.getTitle());
19     }
20
21     @PostUpdate
22     public void logPostUpdate() {
23         logger.info("PostUpdate " + this.getTitle());
24     }
25
26     @PreRemove
27     public void logPreRemove() {
28         logger.info("PreRemove " + this.getTitle());
29     }
30
31     @PostRemove
32     public void logPostRemove() {
33         logger.info("PostRemove " + this.getTitle());
34     }

当然也可以用Entity Listeners �Q�如�Q?br /> 在实体类上加上这个注解：@EntityListeners(value = { MagazineLog.class })
然后写MagazineLog.java:

1 public class MagazineLog {
2     /**
3      * Logger for this class
4      */
5     private static final Logger logger = LoggerFactory.getLogger(MagazineLog.class);
6
7     @PrePersist
8     public void logPrePersist(Object pc) {
9         logger.info("PrePersist " + ((Magazine)pc).getTitle());
10     }
11
12     @PostPersist
13     public void logPostPersist(Object pc) {
14         logger.info("PostPersist " + ((Magazine)pc).getTitle());
15     }
16
17     @PostLoad
18     public void logPostLoad(Object pc) {
19         logger.info("PostLoad " + ((Magazine)pc).getTitle());
20     }
21
22     @PreUpdate
23     public void logPreUpdate(Object pc) {
24         logger.info("PreUpdate " + ((Magazine)pc).getTitle());
25     }
26
27     @PostUpdate
28     public void logPostUpdate(Object pc) {
29         logger.info("PostUpdate " + ((Magazine)pc).getTitle());
30     }
31
32     @PreRemove
33     public void logPreRemove(Object pc) {
34         logger.info("PreRemove " + ((Magazine)pc).getTitle());
35     }
36
37     @PostRemove
38     public void logPostRemove(Object pc) {
39         logger.info("PostRemove " + ((Magazine)pc).getTitle());
40     }
41 }

��p��些，�q�个比较��?br />

天独 2010-04-22 20:01 发表评论

JPA入门-2

天独 — Tue, 06 Apr 2010 14:24:00 GMT

�q�里接上�ơ的一些没有说完的�Q�openJPA�?两个常用属�?br />

�q�两个是比较常用的属�?br /> 今天说的是一对多的关联，�q�里有三个类�Q�非别是User�Q�Post�Q�Comment他们之间的关�p�L��Q�User中有多个Post�? Comment�Q�Post有多个Comment�Q�而Comment有只有一个User和Post�Q�这里我��׃��列出来表�l�构了，因�ؓ可以用JPA的自动生�? �?br /> 下面是User的关键代�?

1 @Entity
2 public class User {
3   @Id
4   @GeneratedValue(strategy = GenerationType.SEQUENCE)
5   private int id;
6   private String name;
7   private String password;
8   private String gender;
9   @OneToMany(cascade = CascadeType.ALL)
10   private List<Comment> comments;
11   @OneToMany(cascade = CascadeType.ALL)
12   private List<Post> posts;
13   // ………………
14 }

没有什么可说的�Q�只说两�?br /> 1.@GeneratedValue(strategy = GenerationType.SEQUENCE)�q�是说�ؓid自动生成一个序列，�q�个选项湖自动在数据库中创徏一个用来生成序列的表，一共有四种

GeneratorType.AUTO: The default. Assign the field a generated value, leaving the details to the JPA vendor.
GenerationType.IDENTITY: The database will assign an identity value on insert.
GenerationType.SEQUENCE: Use a datastore sequence to generate a field value.
GenerationType.TABLE: Use a sequence table to generate a field value

�q�事Apache官方文档说的�Q?英文不好我就不翻译了�Q�应该说的很明白�Q�也很容易懂
GenerationValue�q�有另外一个属性generator�q�个我只在AUTO下实验了�Q�他有下面几�U�：

uuid-string: OpenJPA will generate a 128-bit type 1 UUID unique within the network, represented as a 16-character string. For more information on UUIDs, see the IETF UUID draft specification at: http://www1.ics.uci.edu/~ejw/authoring/uuid-guid/
uuid-hex: Same as uuid-string, but represents the type 1 UUID as a 32-character hexadecimal string.
uuid-type4-string: OpenJPA will generate a 128-bit type 4 pseudo-random UUID, represented as a 16-character string. For more information on UUIDs, see the IETF UUID draft specification at: http://www1.ics.uci.edu/~ejw/authoring/uuid-guid/
uuid-type4-hex: Same as uuid-type4-string , but represents the type 4 UUID as a 32-character hexadecimal string.

2.@OneToMany(cascade = CascadeType.ALL),�U�联�Q�我�q�里是所有，�U�联也是�?中（�q�是考的官方文档�Q�：

CascadeType.PERSIST: When persisting an entity, also persist the entities held in this field. We suggest liberal application of this cascade rule, because if the EntityManager finds a field that references a new entity during flush, and the field does not use CascadeType.PERSIST, it is an error.
CascadeType.REMOVE: When deleting an entity, also delete the entities held in this field.
CascadeType.REFRESH: When refreshing an entity, also refresh the entities held in this field.
CascadeType.MERGE: When merging entity state, also merge the entities held in this field.

具体的还是要看官�Ҏ��档，说的很详�l?br /> �q�里也可以��用其中的几种�Q?�U�或着多重�Q�例如：@ManyToOne(cascade= {CascadeType.PERSIST,CascadeType.REMOVE,CascadeType.REFRESH,CascadeType.MERGE})
下来是Post和Comment的关键代码：

1 @Entity
2 public class Post {
3   @Id
4   @GeneratedValue(strategy = GenerationType.SEQUENCE)
5   private int id;
6   private Date createDate;
7   private String title;
8   private String content;
9   @ManyToOne(cascade = CascadeType.ALL)
10   private User author;
11   @OneToMany(cascade = CascadeType.ALL)
12   private List<Comment> comments;
13   // ………………
14 }
15
16 @Entity
17 public class Comment {
18   @Id
19   @GeneratedValue(strategy = GenerationType.SEQUENCE)
20   private int id;
21   private Date createDate;
22   private String title;
23   private String content;
24   @ManyToOne(cascade = CascadeType.ALL)
25   private User author;
26   @ManyToOne(cascade = CascadeType.ALL)
27   private Post post;
28   // ………………
29 }

下来的应该没有什么可说的�Q�下面是我的��试代码�Q?br />

1  EntityManagerFactory factory = Persistence.createEntityManagerFactory("test");
2 EntityManager em = factory.createEntityManager();
3 em.getTransaction().begin();
4 User user = new User();
5 user.setName("Innate");
6 user.setPassword("Innate");
7 user.setGender("�?/span>");
8 List<Post> posts = new ArrayList<Post>();
9
10 for (int i = 0; i < 5; i++) {
11   Post post = new Post();
12   post.setAuthor(user);
13   post.setContent("test");
14   post.setCreateDate(new Date());
15   post.setTitle("Innate");
16   posts.add(post);
17   List<Comment> comments = new ArrayList<Comment>();
18   for (int j = 0; j < 5; j++) {
19     Comment comment = new Comment();
20     comment.setAuthor(user);
21     comment.setContent("testtest");
22     comment.setCreateDate(new Date());
23     comment.setPost(post);
24     comment.setTitle("InnateInnate");
25     comments.add(comment);
26   }
27   post.setComments(comments);
28   user.setComments(comments);
29 }
30 user.setPosts(posts);
31 em.persist(user);
32 em.getTransaction().commit();

源代码（包含1�Q?的）:JTATest.7z

天独 2010-04-06 22:24 发表评论

JPA入门-1

天独 — Sat, 03 Apr 2010 08:01:00 GMT

�q�里我用的是openJPA
persistence.xml文�g的配�|?br />

1 <persistence-unit name="test">
2   <class>cn.is.test.Testclass>
3
4   <properties>
5     <property name="openjpa.ConnectionURL" value="jdbc:mysql://localhost:3306/test" />
6     <property name="openjpa.ConnectionDriverName" value="com.mysql.jdbc.Driver" />
7     <property name="openjpa.ConnectionUserName" value="root" />
8     <property name="openjpa.ConnectionPassword" value="root" />
9   properties>
10 persistence-unit>

�q�里有个问题�Q�我一般用mysql驱动的org.gjt.mm.mysql.Driver�q�个驱动�c�，但是在这里，�q�行的时候报驱动�c�L��着�q�接URL错误

下面的是实体�c?br />

1 package cn.is.test;
2
3 import java.io.Serializable;
4 import javax.persistence.Entity;
5 import javax.persistence.Id;
6
7 @Entity
8 public class Test implements Serializable {
9   @Id
10   private String id;
11
12   private String userName;
13
14   private String password;
15
16   private String sex;
17
18   private static final long serialVersionUID = 1L;
19
20   public Test() {
21     super();
22   }
23
24   public String getId() {
25     return this.id;
26   }
27
28   public void setId(String id) {
29     this.id = id;
30   }
31
32   public String getUserName() {
33     return this.userName;
34   }
35
36   public void setUserName(String username) {
37     this.userName = username;
38   }
39
40   public String getPassword() {
41     return this.password;
42   }
43
44   public void setPassword(String password) {
45     this.password = password;
46   }
47
48   public String getSex() {
49     return this.sex;
50   }
51
52   public void setSex(String sex) {
53     this.sex = sex;
54   }
55
56
57
58 }
59

下来的是��试代码�Q?br />

1 EntityManagerFactory factory = Persistence.createEntityManagerFactory("test");
2 EntityManager em = factory.createEntityManager();
3 Test test = new Test();
4 test.setId(UUID.randomUUID().toString());
5 test.setSex("�?/span>");
6 test.setUserName("Innate");
7 test.setPassword("solitary");
8
9 em.getTransaction().begin();
10
11 em.persist(test);
12
13 em.getTransaction().commit();
14
15 em.close();
16
17 em = factory.createEntityManager();
18
19 Query query = em.createQuery("select t from Test t");
20 List<Test> testList = query.getResultList();
21
22 for (Test _test : testList) {
23 System.out.println(_test.getUserName());
24 }
25
26 em.close();
27 factory.close();

天独 2010-04-03 16:01 发表评论