JPA關系映射之many-to-many

@ManyToMany

Board表實體類

@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表實體類

@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是多對多映射關系，用@ManyToMany注釋標注。

在Board類中指定我們這個users的集合是映射到User類里面的manBoards屬性列。

在User中用@JoinTable指定中間表，並為該表添加了相關列，其中joinColumns添加該屬性所在User表中的主鍵user_id，inverseJoinColumns添加Board表中的主鍵board_id。