How you shouldn’t write your mapping

More than one time, in my courses, in this blog and in various NH’s users list, I talked about a rule of thumb about mappings: not try to be clear because it obscures.

Have a look to this mapping:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
   <class name="YourApp.Common.DataObjects.Address, YourApp"
          table="Address">
       <id name="Id" type="Int32" unsaved-value="null">
           <column name="Id"
                   length="4" sql-type="int"
                   not-null="true" unique="true" index="PK_Address"/>
           <generator class="native" />
       </id>
       <property name="Address1" type="String">
           <column name="Address1" length="255"
                   sql-type="varchar" not-null="true"/>
       </property>
       <property name="Address2" type="String">
           <column name="Address2" length="255"
                   sql-type="varchar" not-null="false"/>
       </property>
       <property name="City" type="String">
           <column name="City" length="255"
                   sql-type="varchar" not-null="true"/>
       </property>
       <property name="State" type="String">
           <column name="`State`" length="2"
                   sql-type="varchar" not-null="true"/>
       </property>
       <property name="Zip" type="String">
           <column name="Zip" length="12"
                   sql-type="varchar" not-null="true"/>
       </property>
       <many-to-one name="Contact" class="YourApp.Common.DataObjects.Contact, YourApp">
           <column name="Contact_Id" length="4"
                   sql-type="int" not-null="false"/>
       </many-to-one>
       <bag name="BillToOrderHeaders" inverse="true" lazy="true" cascade="all-delete-orphan">
           <key column="BillToAddress_Id"/>
           <one-to-many
               class="YourApp.Common.DataObjects.OrderHeader, YourApp"/>
       </bag>
       <bag name="ShipToOrderHeaders" inverse="true" lazy="true" cascade="all-delete-orphan">
           <key column="ShipToAddress_Id"/>
           <one-to-many
               class="YourApp.Common.DataObjects.OrderHeader, YourApp"/>
       </bag>
   </class>
</hibernate-mapping>

This is how it may look having the same result:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                  assembly="YourApp"
                  namespace="YourApp.Common.DataObjects">
  
   <class name="Address">
       <id name="Id">
           <generator class="native" />
       </id>
       <property name="Address1" not-null="true" />
       <property name="Address2"/>
       <property name="City" not-null="true"/>
       <property name="State" length="2" not-null="true"/>
       <property name="Zip" length="12" not-null="true"/>
       <many-to-one name="Contact" column="Contact_Id"/>
       <bag name="BillToOrderHeaders" inverse="true" cascade="all-delete-orphan">
           <key column="BillToAddress_Id"/>
           <one-to-many class="OrderHeader"/>
       </bag>
       <bag name="ShipToOrderHeaders" inverse="true" cascade="all-delete-orphan">
           <key column="ShipToAddress_Id"/>
           <one-to-many class="OrderHeader"/>
       </bag>
   </class>
</hibernate-mapping>

In this second representation we can understand immediately which are the difference with the NHibernate convention and, over all, you are not hurting your eyes reading it ;-) .