多对多相对于连接表的，有两种
1、使用连接表的单向多对多关联
 <class name="com.jason.associations.many2many.unilateralism.Person" table="Person">
  <id name="id" column="personId">
   <generator class="native"/>
  </id>
  <set name="addresses" table="PersonAddress" cascade="all">
   <key column="personId" not-null="true"/>
   <many-to-many
    column="addressId"
    class="com.jason.associations.many2many.unilateralism.Address"/>
  </set>
  <property name="name" column="personName" type="string" />
 </class>
 
 <class name="com.jason.associations.many2many.unilateralism.Address" table="Address">
  <id name="id" column="addressId">
   <generator class="native"/>
  </id>
  <property name="country" column="country" type="string" />
  <property name="city" column="city" type="string" />
 </class>
 <!--
  create table Person ( personId bigint not null primary key, personName varchar(20))
  create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId))
  create table Address ( addressId bigint not null primary key, country varchar(20), city varchar(20) )
 -->
 

2、使用连接表的双向多对多关联
 <class name="com.jason.associations.many2many.both.Person" table="Person">
  <id name="id" column="personId">
   <generator class="native"/>
  </id>
  <set name="addresses" table="PersonAddress" cascade="all">
   <key column="personId" not-null="true"/>
   <many-to-many
    column="addressId"
    class="com.jason.associations.many2many.both.Address"/>
  </set>
  <property name="name" column="personName" type="string" />
 </class>
 
 <class name="com.jason.associations.many2many.both.Address" table="Address">
  <id name="id" column="addressId">
   <generator class="native"/>
  </id>
  <set name="persons" table="PersonAddress" inverse="false" cascade="all">
   <key column="addressId" not-null="true"/>
   <many-to-many
    column="personId"
    class="com.jason.associations.many2many.both.Person"/>
  </set>
  <property name="country" column="country" type="string" />
  <property name="city" column="city" type="string" />
 </class>
 <!--
  create table Person ( personId bigint not null primary key, personName varchar(20))
  create table PersonAddress ( personId bigint not null, addressId bigint not null, primary key (personId, addressId))
  create table Address ( addressId bigint not null primary key, country varchar(20), city varchar(20) )
 -->