# 7.3.3\. 一对一（one to one） _基于连接表的单向一对一关联_非常少见，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> </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 ) ```