JPA实体关系映射

OneToOne

public classEmployee implements Serializable {

         ……

    @OneToOne(cascade = CascadeType.ALL, orphanRemoval = true, fetch = FetchType.LAZY)

    @JoinColumn(name = "ADDR_ID")

　　private Address address;

… …

}

ManyToOne

public classEmployee implements Serializable {

         ……

    @ManyToOne(fetch = FetchType.LAZY)

    @JoinTable(name = "EMP_JOB", joinColumns = @JoinColumn(name = "EMP_ID"), inverseJoinColumns = @JoinColumn(name = "TITLE_ID"))

    //連接表 joinColumns參考主表的主鍵的列，inverseJoinColumns參考字段或屬性生成的表格的主鍵的列

　　private JobTitle jobTitle;


    @ManyToOne(fetch = FetchType.LAZY)

    @JoinColumn(name = "MANAGER_ID")

　　private Employee manager;

… …

}

OneToMany

public classEmployee implements Serializable {

         ……

    @OneToMany(mappedBy = "manager") //manager字段擁有關係

    private List<Employee> managedEmployees = newArrayList<Employee>();


    @OneToMany(mappedBy = "owner", cascade = CascadeType.ALL, orphanRemoval = true)

　　private List<PhoneNumber> phoneNumbers = newArrayList<PhoneNumber>();


    @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true)

    @JoinColumn(name="EMP_ID")

    private List<Degree> degrees = newArrayList<Degree>();

         ……

}

ManyToMany

public classEmployee implements Serializable {

         ……

    @ManyToMany

    //連接表

    @JoinTable(name = "PROJ_EMP", joinColumns = @JoinColumn(name = "EMP_ID"), inverseJoinColumns = @JoinColumn(name = "PROJ_ID"))

　  private List<Project> projects = newArrayList<Project>();

… …

}

联合主键映射

ManyToOne OneToMany ManyToMany映射，而且采用JoinTable映射，会出现联合主键，即双主键。