好的，我看正常做有什么问题。

<class name="City" table="CITY">
    <id name="id" type="integer">
      <generator class="native" />
    </id>
    <property name="name" />
</class>
<class name="Distance" table="DISTANCE">
    <id name="id" type="integer">
      <generator class="native" />
    </id>
    <many-to-one name="city" column="cityId" class="City"/>
    <many-to-one name="neighbour" column="neighbourId" class="City"/>
</class>

也没测试过。

像这样的怎么样

<class name="City" table="CITIES">
    <id name="id" type="integer">
      <generator class="native" />
    </id>
    <property name="name" />
    <set name="neighbours" table="DISTANCES">      
        <key column="city_id" />
        <many-to-one name="neighbour" class="City" />
    </set>
</class>

但没有测试。