<set name="orders" table="O2_customer">
<key>
<column name="cid"></column>
</key>
<one-to-many class="com.itheima.a_primer.oneToManyDouble.Order"/>
</set>
<key>
<column name="cid"></column>
</key>
<one-to-many class="com.itheima.a_primer.oneToManyDouble.Order"/>
</set>