Why can't I create child objects in Hibernate/NHibernate - tricky mapping problem

Question

I think I have tried every thing to get this to work but to no avail. Any hints/help much appreciated.

The following parent-children relationship causes the following error on creation of the parent.

could not insert: [Kanpeki.Domain.CalEvtCatergory][SQL: INSERT INTO tb_calEvent_catergory (catergoryID, parentID, catergoryType, catergoryLabel, id) VALUES (?, ?, ?, ?, ?)]

The 2 object mappings are as follows:

Parent = CalEvent

  <id name="id" column="id">
  <generator class="hilo"/>
</id>

<bag name="catergories" table="tb_calEvent_catergory"  lazy="false" cascade="all">
  <key column="parentID" foreign-key="id"/>
  <one-to-many class="CalEvtCatergory"/>
</bag>

Child = CalEvtCatergory

  <class name="CalendarCatergory" table="tb_calendar_catergory" lazy="false" >

<id name="id" column="id">
  <generator class="hilo"/>
</id>

<property name="parentID" />
snip....

It doesn't seem to be applying the (parentID) id of the calEvent to the CalendarCatergory

Answer 1

What does your c# (or vb) code look like when you are creating the new category?

Answer 2

It sounds like it's probably trying to insert a NULL into a parent_id column on the child table that is marked as not null. There are two things you should do that will (probably) fix your problem. First, change

<property name="parentID" />

to

<many-to-one name="parentID" column="parent_id_column_name_here" not-null="true" />

Then, mark the relationship as inverse (i.e. the child manages the state of the relationship via the parentID property) by adding inverse="true" to the bag on the parent like:

<bag name="catergories" table="tb_calEvent_catergory" inverse="true" lazy="false" cascade="all">
  <key column="parentID" foreign-key="id"/>
  <one-to-many class="CalEvtCatergory"/>
</bag>

Also, I'm not sure the bag mapping is correct. Specifically, the foreign-key attribute. I couldn't find this in the documentation. NHibernate probably just ignores it but I'd get rid of it. In general, bi-directional, one-to-many mappings should look like:

<!-- Parent Table Mapping -->
...
<set name="Children" inverse="true" [(optional)cascade="all|save-update|etc"]>
    <key column="parent_id" />
    <one-to-many class="Child" />
</set>
...

<!-- Child Table Mapping -->
...
<many-to-one name="Parent" column="parent_id" not-null="true"/>
...

If you don't specify cascading, you have to save each object individually.