JPA 實體映射

一、實體基本映射

 1 /*
 2 * @Entity:將領域對象標註為一個實體,表示保存到資料庫中
 3 * @@Table:保存到資料庫中表名,預設表名為類名,可通過name屬性命名
 4 *
 5 * */
 6 @Entity
 7 @Table(name="t_user")
 8 public class User {
 9 
10 
11     @Id //主鍵
12     @GeneratedValue // JPA自動選擇合適的生成策略
13     @Column(name="id_") //列名,預設為屬性名,可通過name屬性指定列名
14     private Integer id;    
15     
16     
17 /*    @Id
18     @GeneratedValue(generator="uuidGenerator")
19     @GenericGenerator(name="uuidGenerator",strategy="uuid") //UUID生成策略
20     @Column(name="id_",length=32)
21     private String id;*/
22     
23     
24 /*    @Id
25     @GeneratedValue(strategy = GenerationType.AUTO) //JPA自動選擇合適的策略,是預設選項
26     @Column(name="id_")
27     private Integer id;*/
28     
29         
30     /*
31      *     
32     @Id
33     @GeneratedValue(strategy=GenerationType.IDENTITY) //表示自增鍵欄位,oracle不支持這種方式
34     @Column(name="id_")
35     private Integer id;*/
36     
37     
38     /*    
39     @Id
40     @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "idGenerator") //通過序列產生主鍵,通過@SequenceGenerator註解指定序列列名,mysql不支持這種方式
41     @SequenceGenerator(name = "idGenerator",sequenceName="mySeq",allocationSize=1)
42     @Column(name="id_")
43     private Integer id;*/    
44     
45     /*    
46     @Id
47     @GeneratedValue(strategy = GenerationType.TABLE, generator = "userGenerator")//通過表產生主鍵，框架藉由表模擬序列產生主鍵，使用該策略可以使應用更易於資料庫移植。
48     @TableGenerator(name = "userGenerator",table="pk_generator",
49                     pkColumnName="gen_name",
50                     valueColumnName="gen_value",
51                     pkColumnValue="user_pk",
52                     initialValue=0,
53                     allocationSize=1)
54     @Column(name="id_")
55     private Integer id;    
56     */
57 
58     //length:欄位的長度;nullable:是否允許為空;unique:指定是否唯一性;insertable updatable:指定該欄位是否插入或修改到資料庫表中,對應表中需通過columnDefinition指定預設值;
59     @Column(name="name_", length=60, nullable=false,unique=true,insertable=false,updatable=false)
60     private String name;
61     
62     @Column(name="address_", length=60, nullable=false)
63     private String address;
64     
65     @Column(name="phone_", length=11, nullable=true,columnDefinition="CHAR(10) default '000'") //columnDefinition:底層資料庫的欄位類型,根據不同資料庫配置
66     private String phone;
67     
68     @Column(name="inCome_", precision=12, scale=2) //precision:浮點型總長度;scale:小數的位數
69     private BigDecimal inCome;
70     
71     @Temporal(TemporalType.DATE) //如果屬性是時間類型，因為數據表對時間類型有更嚴格的劃分，所以必須指定具體時間類型。
72     private Date birthday;
73     //Date 日期型，精確到年月日，例如“2008-08-08”
74     //Time 時間型，精確到時分秒，例如“20:00:00”
75     //Timestamp 時間戳，精確到納秒，例如“2008-08-08 20:00:00.000000001”
76     
77     @Lob
78     @Column(name="pic_")
79     @Basic(fetch=FetchType.LAZY)
80     private byte[] pic;
81     
82     @Lob
83     @Column(name="note_")
84     @Basic(fetch=FetchType.LAZY)
85     private String note;
86     
87     ...........
88 }    

二、實體表間映射

1、一對一實體映射：人與地址

 1 @Entity
 2 public class Person {
 3     @Id 
 4     @GeneratedValue(strategy = GenerationType.AUTO) 
 5     private Long id; 
 6     private String name;
 7     private int age;
 8     //@OneToOne 一對一映射,級聯操作，通過cascade屬性設置；懶載入操作，通過fetch屬性設置
 9     @OneToOne(cascade={CascadeType.REFRESH,CascadeType.REMOVE},fetch=FetchType.LAZY)
10     //@JoinColumn:Person中address欄位對應的"address_id"表示Address中"aid"欄位,即外鍵關係;如自動建表,@JoinColum註解可省略
11     @JoinColumn(name="address_id",referencedColumnName="aid")
12     //@JoinColumns(value={@JoinColumn(name="address_id",referencedColumnName="aid"),@JoinColumn(name="address_id2",referencedColumnName="aid2")})
13     private Address address;
14 ...........
15 }

 1 @Entity
 2 public class Address {
 3 
 4     @Id
 5     @GeneratedValue(strategy = GenerationType.AUTO)
 6     private Long aid;
 7     private String street;
 8     private String city;
 9     private String country;
10     
11 
12     @Column(name="aid_")
13     public Long getAid() {
14         return aid;
15     }
16 .............
17 }

2、一對多實體映射：員工表與部門表

 1 @Entity
 2 public class Depart {
 3     @Id
 4     @GeneratedValue
 5     private Long did;
 6     private String name;
 7 
 8     @OneToMany //一對多映射
 9     /*
10         通過中間表關聯
11       @JoinTable 配置中間表信息,name:中間表名;
12        joinColumns:部門表與中間表間的關係,"depart_id"部門表中的主鍵欄位作為中間表中外鍵(did)欄位
13        inverseJoinColumns:被擁有者,即員工表與中間表的關係
14     */
15     @JoinTable(name = "depart_employee", 
16         joinColumns = @JoinColumn(name = "depart_id",referencedColumnName="did"), 
17         inverseJoinColumns = @JoinColumn(name = "employee_id",referencedColumnName="eid"))
18     /*
19         通過設置外鍵關聯
20         設置"did"欄位做為另一方的外鍵"depart_id"
21     @JoinColumn(name="depart_id",referencedColumnName="did")
22     */
23     private List<Employee> employees;
24 .....
25 }

1 @Entity
2 public class Employee {
3     @Id 
4     @GeneratedValue(strategy = GenerationType.AUTO) 
5     private Long eid; 
6     private String  name;
7 .......
8 }

3、多對多實體映射：老師與學生

 1 @Entity
 2 public class Teacher {
 3 
 4     @Id 
 5     @GeneratedValue(strategy = GenerationType.AUTO) 
 6     private Long tid; 
 7     private String name; 
 8     private Boolean gender; 
 9     private int age; 
10     private int height; 
11     @ManyToMany 
12     @JoinTable(name = "teacher_student", 
13         joinColumns = @JoinColumn(name = "teacher_id",referencedColumnName="tid"), 
14         inverseJoinColumns = @JoinColumn(name = "student_id",referencedColumnName="sid"))
15     private List<Student> students;
16 ..........
17 }

 1 @Entity
 2 public class Student {
 3 
 4     @Id 
 5     @GeneratedValue(strategy = GenerationType.AUTO) 
 6     private Long sid; 
 7     private String name; 
 8     private Boolean gender; 
 9     private int age; 
10     private int height;
11     
12     @ManyToMany(mappedBy = "students") 
13     private List<Teacher> teachers; 
14 ...............
15 }