Hibernate 关联关系映射 -双向关联

 

双向关联（Bidirectional associations）双方都持有对方的引用

 

一对多（one to many) / 多对一（many to one）

双向多对一关联 是最常见的关联关系。（这也是标准的父/子关联关系。）

一边是一对多，另一边是 多对一，分别编写。 

<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <many-to-one name="address"
        column="addressId"
        not-null="true"/>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <set name="people" inverse="true">
        <key column="addressId"/>
        <one-to-many class="Person"/>
    </set>
</class>

<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses"
        table="PersonAddress">
        <key column="personId"/>
        <many-to-many column="addressId"
            unique="true"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress"
        inverse="true"
        optional="true">
        <key column="addressId"/>
        <many-to-one name="person"
            column="personId"
            not-null="true"/>
    </join>
</class>

create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null, addressId bigint not null primary key )
create table Address ( addressId bigint not null primary key )

Person 中是一对多 所以有个<set> 集合， <key >-->personId ,对多 <many-to-many>+unique+

还要加个class

Address中是 多对一，用<join> 加个表,多对一是<many-to-one>

一对一（one to one）

基于连接表的双向一对一关联

极为罕见，但也是可行的。

<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress"
        optional="true">
        <key column="personId"
            unique="true"/>
        <many-to-one name="address"
            column="addressId"
            not-null="true"
            unique="true"/>
    </join>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <join table="PersonAddress"
        optional="true"
        inverse="true">
        <key column="addressId"
            unique="true"/>
        <many-to-one name="person"
            column="personId"
            not-null="true"
            unique="true"/>
    </join>
</class>

create table Person ( personId bigint not null primary key )
create table PersonAddress ( personId bigint not null primary key, 
                                        addressId bigint not null unique )
create table Address ( addressId bigint not null primary key )
  
  
  
  

   
   
   
   
 
    
 
     
多对多（many to many）
 
    
 
   
  
  
  
  
最后，还有 双向多对多关联.
<class name="Person">
    <id name="id" column="personId">
        <generator class="native"/>
    </id>
    <set name="addresses"  table="PersonAddress">
        <key column="personId"/>
        <many-to-many column="addressId"
            class="Address"/>
    </set>
</class>

<class name="Address">
    <id name="id" column="addressId">
        <generator class="native"/>
    </id>
    <set name="people" inverse="true"  table="PersonAddress">
        <key column="addressId"/>
        <many-to-many column="personId"
            class="Person"/>
    </set>
</class>