NHibernate Pitfalls: Many to Many and Inverse
This is part of a series of posts about NHibernate Pitfalls. See the entire collection here.
When you have a many to many relation in NHibernate, you can only set inverse to false on one side of the relation, not on both:
1: <?xml version="1.0" encoding="utf-8"?>
2: <hibernate-mapping default-lazy="false" namespace="SomeNamespace" assembly="SomeAssembly" xmlns="urn:nhibernate-mapping-2.2">
3: <class name="User" lazy="false" table="`USER`">
4: <id name="UsrId" access="property" column="`USR_ID`">
5: <generator class="hilo" />
6: </id>
7: <set cascade="all-delete-orphan" inverse="true" lazy="true" name="Notifications" table="`NOT_USR`">
8: <key column="`USR_ID`" />
9: <many-to-many class="Notification" column="`NOT_ID`" />
10: </set>
11: </class>
12: </hibernate-mapping>
And:
1: <?xml version="1.0" encoding="utf-8"?>
2: <hibernate-mapping default-lazy="false" namespace="SomeNamespace" assembly="SomeAssembly" xmlns="urn:nhibernate-mapping-2.2">
3: <class name="Notification" lazy="false" table="`NOTIFICATION`">
4: <id name="NotificationId" access="property" column="`NOT_ID`">
5: <generator class="hilo" />
6: </id>
7: <property name="Comment" column="`COMMENT`" type="String" length="50"/>
8: <set cascade="all-delete-orphan" lazy="true" name="Users" table="`NOT_USR`">
9: <key column="`NOT_ID`" />
10: <many-to-many class="User" column="`USR_ID`" />
11: </set>
12: </class>
13: </hibernate-mapping>
If you don’t, you won’t be able to save any associations.
