@Formula

@Formula calculate temporary attribute.

Equivalent can be associated with the query field, then placed the entity as a property use.

 

Task: In the User physical layer, add an additional property to get the name field in the Test table.

1 table structure

User表

Test table

2 User physical layer (not part of the field.)

@Entity
@Table(name = "user", catalog = "testdb")
@DynamicUpdate
public class User {
    private Integer id;
    private String uuid;
 
    private String test;
 
    @Id
    @GeneratedValue
    @Column(name = "id")
    public Integer getId() {
        return id;
    }
 
    public void setId(Integer id) {
        this.id = id;
    }
 
    @Column(name = "uuid")
    public String getUuid() {
        return uuid;
    }
 
    public void setUuid(String uuid) {
        this.uuid = uuid;
    }
 
    
    @Formula("(select t.name from test as t where t.id=id)")
    public String getTest() {
        return test;
    }
 
    public void setTest(String test) {
        this.test = test;
    }
}

We can see that in the getTest, an increase of @Formula comment. When the lookup table will be associated with the name Test table to the property.

note:

First, increase the alias table.

Second, pay attention to the two sql parentheses ()

Finally, the last t.id = id id, corresponding to @Colun (value = "id") on the property

 

3 Create a dao by jpa

@Repository
public interface UserDao extends JpaRepository<User,Integer> {
}

4 Test

@Autowired
    private UserDao userDao;
 
    @Test
    public void contextLoads() {
        System.out.println(userDao.findById(2).get().getTest());
    }