JPA关系映射之many-to-many

@ManyToMany

Board表实体类

@Entity
@Cache(usage=CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
@Table(name="t_board")
public class Board extends BaseDomain {
    private int boardId;
    private Set<User> users=new HashSet<User>();

    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    @Column(name="board_id")
    public int getBoardId() {
        return boardId;
    }

    public void setBoardId(int boardId) {
        this.boardId = boardId;
    }
    @ManyToMany(cascade={CascadeType.PERSIST,CascadeType.MERGE}, mappedBy = "manBoards", fetch = FetchType.LAZY)
    public Set<User> getUsers() {
        return users;
    }

    public void setUsers(Set<User> users) {
        this.users = users;
    }
}

User表实体类

 @Entity
 @Cache(usage=CacheConcurrencyStrategy.NONSTRICT_READ_WRITE)
 @Table(name="t_user")
 public class User extends BaseDomain {

     private int userId;
     private Set<Board> manBoards=new HashSet<Board>();

     @Id
     @GeneratedValue(strategy = GenerationType.IDENTITY)
     @Column(name = "user_id")
     public int getUserId() {
         return userId;
     }

     public void setUserId(int userId) {
         this.userId = userId;
     }

     @ManyToMany(cascade={CascadeType.MERGE,CascadeType.PERSIST},fetch=FetchType.EAGER)
     @JoinTable(name="t_board_manager",joinColumns={@JoinColumn(name="user_id")},inverseJoinColumns={@JoinColumn(name="board_id")})
     public Set<Board> getManBoards() {
         return manBoards;
     }

     public void setManBoards(Set<Board> manBoards) {
         this.manBoards = manBoards;
     }

 }

User和Board是多对多映射关系，用@ManyToMany注释标注。

在Board类中指定我们这个users的集合是映射到User类里面的manBoards属性列。

在User中用@JoinTable指定中间表，并为该表添加了相关列，其中joinColumns添加该属性所在User表中的主键user_id，inverseJoinColumns添加Board表中的主键board_id。