# 7.3.2\. 多对一（many to one） _基于连接表的单向多对一关联_在关联关系可选的情况下应用也很普遍。 ``` <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"/> </join> </class> <class name="Address"> <id name="id" column="addressId"> <generator class="native"/> </id> </class> ``` ``` create table Person ( personId bigint not null primary key ) create table PersonAddress ( personId bigint not null primary key, addressId bigint not null ) create table Address ( addressId bigint not null primary key ) ```