Middle.hbm.xml

<?xml version="1.0" encoding="UTF-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">

    <class 
		name="NHibernate.DomainModel.Inner, NHibernate.DomainModel" 
		table="CID_IN"
	>
        <composite-id name="Id">
            <key-property 
				name="AKey" 
				type="String(10)" 
				length="10" 
				column="AKEY"
			/>
            <key-property 
				name="BKey" 
				type="String(10)" 
				length="10" 
				column="BKEY"
			/>
        </composite-id>
        
        <property 
			name="Dudu" 
			length="10" 
			column="DUDU" 
			not-null="true" 
			type="String(10)"
		/>
		
    </class>

    <class 
		name="NHibernate.DomainModel.Middle, NHibernate.DomainModel" 
		table="CID_MID"
	>
        <composite-id name="Id">
            <key-many-to-one name="Sup">
                <column 
					length="10" 
					name="AKEY"
				/>
                <column 
					length="10" 
					name="BKEY"
				/>
            </key-many-to-one>
            <key-property 
				name="One" 
				type="String(10)" 
				length="10" 
				column="ONE"
			/>
            <key-property 
				name="Two" 
				type="String(10)" 
				length="10" 
				column="TWO"
			/>
        </composite-id>
        <property 
			column="BLA" 
			length="10" 
			name="Bla" 
			not-null="true" 
			type="String(10)"
		/>
    </class>

    <class 
		name="NHibernate.DomainModel.Outer, NHibernate.DomainModel" 
		table="CID_OUT"
	>
        <composite-id name="Id">
            <key-many-to-one name="Master">
                <column name="AKEY"/>
                <column name="BKEY"/>
                <column name="ONE"/>
                <column name="TWO"/>
            </key-many-to-one>
            <key-property 
				name="DetailId" 
				type="String(10)" 
				column="ID" 
				length="10"
			/>
        </composite-id>
        <property 
			name="Bubu" 
			column="BUBU" 
			length="10" 
			type="String(10)"
		/>
    </class>

</hibernate-mapping>