【hibernate框架】关系映射之一对一单项外键关联(Annotation实现)

一对一单向外键关联(Annotation做法)：

例子，假设一夫配一妻(Husband与Wife)。两个实体类的例子：

Husband.java:

package cn.edu.hpu.one2one;


import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.OneToOne;


@Entity
public class Husband {
  private int id;
  private String name;
  private Wife wife;


  @Id
  @GeneratedValue
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  
  @OneToOne  //在数据库中会生成Wife_id字段
  public Wife getWife() {
    return wife;
  }
  public void setWife(Wife wife) {
    this.wife = wife;
  }
  
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  } 
  
}

Wife.java:

package cn.edu.hpu.one2one;


import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;


@Entity
public class Wife {
  private int id;
  private String name;


  @Id
  @GeneratedValue
  public int getId() {
    return id;
  }
  public void setId(int id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  } 
}

剖析：在实体类中，Husband有Wife的引用，而Wife里面没有，这就构成了一对一单向关联。如何建表呢？

有关于建表，可以这样思考：

肯定是两张表，一张表示wife，一张表是husband。

husband： id(int)<pk,fk>、name(char)、wife_id<fk>（pk_Reference_1->wife(主键关联)）

wife： id(int)<pk>、name(char) 

也可以设计关联表，即husband和wife的对应表(这里就不建立了)

HusBand_Wife：Hus_id int <fk1>、Wif_id int <fk2>

在测试例子中用SchemaExport来建表，成功。

@Test

 public void testSchemaExport(){

new SchemaExport(new AnnotationConfiguration().configure()).create(true, true);

 }

打印出的建表语句为：

alter table Husband 

         drop 

         foreign key FKAEEA401B45202E0A


     drop table if exists Husband


     drop table if exists Wife


     create table Husband (

         id integer not null auto_increment,

         name varchar(255),

         wife_id integer,

         primary key (id)

     )


     create table Wife (

         id integer not null auto_increment,

         name varchar(255),

         primary key (id)

     )


     alter table Husband 

         add index FKAEEA401B45202E0A (wife_id), 

         add constraint FKAEEA401B45202E0A 

         foreign key (wife_id) 

         references Wife (id)

schema export complete

@OneToOne有哪些属性可以使用呢？

有cascade、fetch、mappedBy、optional、targetEntity。

不想使用hibernate默认的外键的名字“wife_id”,就用Annotation中的@JoinColumn来指定你想要的外键的字段名。

示例：

@OneToOne
@JoinColumn(name="wifeid")
public Wife getWife() {
  return wife;
}

数据库中husband的外键字段名就变为"wifeid"

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