Hibernate的关联关系注解映射(一对一、一对多、多对一、多对多、自连接)

Hibernate注解的关联关系映射,分为2种,即单向关联映射和双向关联映射,它们最大的区别就是在查询数据时,单向关联只能通过一边进行查询,而双向关联两边都可以进行查询。

单向关联是指只在一方加上注解,

双向关联是指双方都加上注解。这里主要记录双向关联。


1.  一对一关联:

如有2张表,公民表Person和身份证表IdCard

一方(IdCard):

@OneToOne(fetch=FetchType.LAZY,//延迟加载
targetEntity=IdCards.class,//目标对象
mappedBy="person",//指定由哪边维护关系(在这指有Person表维护,‘person’指IdCards标中关联的Person对象
cascade=CascadeType.ALL)

另一方(Person):

@OneToOne(fetch=FetchType.LAZY,
targetEntity=Person.class)//维护关系表
@JoinColumn(name="personId",referencedColumnName="personId",unique=true)

具体如下:

@Entity
@Table(name = "tb_person")
public class Person implements Serializable {

	private static final long serialVersionUID = 576770011136181361L;

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long personId;
	@OneToOne(fetch=FetchType.LAZY,targetEntity=IdCards.class,mappedBy="person",cascade=CascadeType.ALL)
	private IdCard idcard;

@Entity
@Table(name = "tb_idcard")
public class Idcard implements Serializable {

	private static final long serialVersionUID = 576770011136181369L;

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long idcardId;
	@OneToOne(fetch=FetchType.LAZY,
	targetEntity=Person.class)
	@JoinColumn(name="personId",referencedColumnName="personId",unique=true)
	private Person person;


2. 一对多关系:

       一方:

@OneToMany(fetch=FetchType.LAZY,

targetEntity=User.class,

cascade=CascadeType.ALL,

orphanRemoval=true,//孤儿删除

mappedBy="department")

   cascade=CascadeType.ALL,,即交由多的一方控制;
多方:


            @ManyToOne(fetch = FetchType.LAZY,targetEntity = Department.class)@JoinColumn(name = "departmentId",referencedColumnName="departmentId")
	如:一个用户只能属于一个部门,一个部门里可以有很多用户,其注解如下,
部门实体类:
@Entity
@Table(name = "tb_department")
public class Department implements Serializable {

    private static final long serialVersionUID = -3489189232910430049L;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long departmentId;

    private String name;

    private String description;

	@OneToMany(fetch=FetchType.LAZY,targetEntity=User.class,cascade=CascadeType.ALL,orphanRemoval=true,mappedBy="department")
	private Set<User> users;
       ........
}

用户实体类:
@Entity
@Table(name="tb_user")
public class User implements Serializable {

    private static final long serialVersionUID = 576770011136181361L;

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long userId;

   	@ManyToOne(fetch = FetchType.LAZY,targetEntity = Department.class)
	@JoinColumn(name = "departmentId",referencedColumnName="departmentId")
	private Department department;

    private String loginName;
      ........
       ........
}


2. 多对多关系:

          多方:

@ManyToMany(fetch=FetchType.LAZY,targetEntity=Role.class)@JoinTable(name = "tb_user_role", joinColumns = @JoinColumn(name = "userId",referencedColumnName="userId") , inverseJoinColumns = @JoinColumn(name = "roleId",referencedColumnName="roleId"))

其中“tb_user_role”是两者的关系表,由两者的主键ID组成。通过@JoinColumn(name = "userId")指定在关系表中的字段名。

另一个多方:

@ManyToMany(fetch = FetchType.LAZY, targetEntity = User.class, cascade = CascadeType.ALL, mappedBy = "roles")

joinColumns :指主表,inverseJoinColumns :指匹配表
即user-->role,则user是主表,role是匹配表


如:一个用户可以有多个角色,一个角色可以适用于多个用户。

用户实体类:

@Entity
@Table(name="tb_user")
public class User implements Serializable {

	private static final long serialVersionUID = 576770011136181361L;

	@Id
	@GeneratedValue(strategy=GenerationType.AUTO)
	private Long userId;

	private String loginName;

	private String name;

	private String gender;

	private String phone;

	private String email;

	private String description;
	
	@ManyToMany(fetch=FetchType.LAZY,targetEntity=Role.class)
	@JoinTable(name = "tb_user_role", joinColumns = @JoinColumn(name = "userId",referencedColumnName="userId") , 
	inverseJoinColumns = @JoinColumn(name = "roleId",referencedColumnName="roleId"))
	private Set<Role> roles = new HashSet<Role>();     
        .....
}


角色实体类: 

@Entity
@Table(name = "tb_role")
public class Role implements Serializable {

	private static final long serialVersionUID = -7625883839295666830L;

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long roleId;

	private String name;

	private String description;

	@ManyToMany(fetch = FetchType.LAZY, targetEntity = User.class, cascade = CascadeType.ALL, mappedBy = "roles")
	private Set<User> users = new HashSet<User>();
        .....
        .....
}


2. 自连接关系:

自连接一方:

@ManyToOne(fetch = FetchType.LAZY, targetEntity = Department.class)
@JoinColumn(name = "parentId",referencedColumnName="departmentId")

自连接多方:

@OneToMany(fetch=FetchType.LAZY,targetEntity=Department.class,cascade=CascadeType.ALL,orphanRemoval=true,mappedBy="parent")
@OrderBy("departmentId ASC")

     因为是自连接,在一个表里操作,表中要增加一个父类id,用户建立连接。

   如:部门管理,一个部门可以有很多个下级部门,但是一个上级部门只能有一个上级部门,这时需要建立自连接。

部门实体类::

@Entity
@Table(name = "tb_department")
public class Department implements Serializable {

	private static final long serialVersionUID = -3489189232910430049L;

	@Id
	@GeneratedValue(strategy = GenerationType.AUTO)
	private Long departmentId;

	private String name;

	private String description;
       
	@ManyToOne(fetch = FetchType.LAZY, targetEntity = Department.class)
	@JoinColumn(name = "parentId",referencedColumnName="departmentId")
	private Department parent;


	@OneToMany(fetch=FetchType.LAZY,targetEntity=Department.class,cascade=CascadeType.ALL,orphanRemoval=true,mappedBy="parent")
	@OrderBy("departmentId ASC")
	private Set<Department> children = new HashSet<Department>();
	....
        .....
}
 




  




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