diff --git a/03/src/de/dis2013/data/mapping/Contract.hbm.xml b/03/src/de/dis2013/data/mapping/Contract.hbm.xml
index b4718ec..fa71d66 100644
--- a/03/src/de/dis2013/data/mapping/Contract.hbm.xml
+++ b/03/src/de/dis2013/data/mapping/Contract.hbm.xml
@@ -12,13 +12,13 @@
 		<many-to-one name="vertragspartner" class="de.dis2013.data.Person" column="person" not-null="true" />
 
 		<joined-subclass name="de.dis2013.data.Kaufvertrag" table="purchasecontract" schema="VSISP12">
-        	<key column="id"/>
+        	<key column="contractnumber"/>
 			<property name="anzahlRaten" type="integer" column="numberofinstallments" />
 			<property name="ratenzins" type="integer" column="interestrate" />
 			<many-to-one name="haus" class="de.dis2013.data.Haus" column="house" not-null="true" />
 		</joined-subclass>
 		<joined-subclass name="de.dis2013.data.Mietvertrag" table="tenancycontract" schema="VSISP12">
-        	<key column="id"/>
+        	<key column="contractnumber"/>
 			<property name="mietbeginn" type="date" column="startdate" />
 			<property name="dauer" type="date" column="duration" />
 			<property name="nebenkosten" type="integer" column="additionalcosts" />