Hibernate关系投射( 双向关联XML )

Hibernate关系映射( 双向关联XML )
一:使用连接表的双向关联
1: 一对多（one to many)/多对一（many to one）
下面是一个基于连接表的双向一对多关联的例子。注意 inverse="true" 可以出现在关联的任意一端，即 collection 端或者 join 端。

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.hbm.xml:

<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>

address.hbm.xml:

<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>

2:一对一（one to one）基于连接表的双向一对一关联也是可行的，但极为罕见。

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 )

person.hbm.xml:

<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>

address.hbm.xml:

<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>

3:多对多（many-to-many）
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