通過Hibernate關聯表檢索對象？

Question

有三個表A，B，A_B_relation，最後一個是A的關聯表和B.

Columns of table A:    id, value_a 
Columns of table B:    id, value_b 
Columns of table A_B_relation: id, a_id, b_id 

您可能會發現A和B作爲下面的映射類。請注意，有一個領域「B B」類A.

@Entity 
@Table(name = "A") 
public class A { 

    @GenericGenerator(name = "idGenerator", strategy = "increment") 
    @Id 
    @GeneratedValue(generator = "idGenerator") 
    @Column(name = "id", unique = true, nullable = false) 
    private Integer id; 

    @Column(name = "value_a") 
    private String valueA; 

    private B b; 
} 

@Entity 
@Table(name = "B") 
public class B { 

    @GenericGenerator(name = "idGenerator", strategy = "increment") 
    @Id 
    @GeneratedValue(generator = "idGenerator") 
    @Column(name = "id", unique = true, nullable = false) 
    private Integer id; 

    @Column(name = "value_b") 
    private String valueB; 
} 

是否有可能在休眠session.get("A", id)獲得實例的初始化與B'據我所知，應該有表連接，如A a left join A_B_relation r on a.id = r.a_id left join B b on r.b_id = b.id，但我不知道如何通過休眠來實現它。

在此先感謝。

Answer 1

因爲你沒有描述A和B之間的關係，它是OneToOne ManyToOne OneToMany ManyToMany我會認爲它是從A側的ManyToOne，因爲每個A只與一個B有關，而你需要第三個表使聯接所以每個A與一個B相關，但B可以與多個A相關聯

@Entity 
    @Table(name = "A") 
    public class A { 

     @GenericGenerator(name = "idGenerator", strategy = "increment") 
     @Id 
     @GeneratedValue(generator = "idGenerator") 
     @Column(name = "id", unique = true, nullable = false) 
     private Integer id; 

     @Column(name = "value_a") 
     private String valueA; 
     @joinTable(name="A_B_relation",joinColumns=@JoinColumn(name="a_id"), 
        inverseJoinColumns=@JoinColumn(name="b_id")) 
     @ManyToMany(fetch=FetchType.EAGER) 
     private List<B> b; 
    }