Help needed with many-to-one nullable relationship

bengdell · **Joined:** Tue Jan 08, 2008 7:58 am **Posts:** 3

Hey guys,

Hoping you can help me with this problem. it's really starting to get a little annoying. I'm sure it's something i'm missing in the mapping files, but i just can't seem to sort it.

Basically I've got a table that has a NULLABLE foreign key. As far as i know the mapping files for both tables have been set-up properly (you can see each of these below). Each table knows of the other etc. (many-to-one and one-to-many)... however, when i try and save the many-to-one table WITHOUT a value set in the foreign key table it fails giving a standard SQL error message saying that there was a foreign key constraint problem.

This is of course an error message i would expect to receive if either:

a) the foreign key did NOT accept nulls or
b) i had set the foreign key ID to one that doesn't exist

Neither of these are true. in fact to make sure i've set the objectA.objectB = null. just in case nhibernate is trying to set it's value to zero or something.

Any ideas people? I'm sure it's just something i've missed in the mapping files.... which can be seen below:

ContentField.xml

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="App.Domain.Classes" assembly="App.Domain" default-access="property">
   <class name="App.Domain.Classes.EntityField, App.Domain" table="EntityField">
      <id name="Id" type="Int32" unsaved-value="null">
         <column name="EntityFieldID" length="4" sql-type="int" not-null="true" unique="true" index="PK_ContentEntryField"/>
         <generator class="identity" />
      </id>
      <many-to-one name="ContentEntry" class="App.Domain.Classes.ContentEntry, App.Domain">
         <column name="ContentEntryId" length="4" sql-type="int" not-null="false"/>
      </many-to-one>
   </class>
</hibernate-mapping>

ContentEntry.xml

Code:

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="App.Domain.Classes" assembly="App.Domain" default-access="property">
   <class name="App.Domain.Classes.ContentEntry, App.Domain" table="ContentEntry">
      <id name="Id" type="Int32" unsaved-value="null">
         <column name="ContentEntryId" length="4" sql-type="int" not-null="true" unique="true" index="PK_ContentEntry"/>
         <generator class="identity" />
      </id>
      <bag name="EntityFields" inverse="true" lazy="true" cascade="all-delete-orphan">
         <key column="ContentEntryId"/>
         <one-to-many  class="App.Domain.Classes.EntityField, App.Domain"/>
      </bag>
   </class>
</hibernate-mapping>

It is the ContentField table that i am trying to create a record for without the ContentEntry foreign key set...

Looking forward to your replies and help.

Ben

mabraham · **Joined:** Mon Mar 20, 2006 10:49 pm **Posts:** 59

I suspect that the problem is that the foreign key that you want to be null is not a nullable type, i.e., it's an int. So it's being persisted as a zero, which is an invalid foreign key value.

jta · **Posted:** Wed Jan 09, 2008 1:25 pm

Try to look at the SQL nHibernate Executes and see which value is supplied for your NULLABLE parameter

bengdell · **Joined:** Tue Jan 08, 2008 7:58 am **Posts:** 3

If a zero is being applied for some reason, what do you suggest i do? Can you suggest what additional parameters i would need to add to the mapping xml file?

marcal · **Posted:** Wed Jan 09, 2008 4:32 pm

mabraham wrote:

I suspect that the problem is that the foreign key that you want to be null is not a nullable type, i.e., it's an int. So it's being persisted as a zero, which is an invalid foreign key value.

But NH is smart enough to figure that out for an FK on a many-to-one. This is something that should work out of the box, so something else must be going on. Configure log4net to get all the SQL that NH is executing (it's all under the NHibernate.SQL logger).

The only thing fishy about your mappings is that they seem way overdone. Try paring them down to default and detected settings and see if that helps.

bengdell · **Joined:** Tue Jan 08, 2008 7:58 am **Posts:** 3

From what you can see is there anything specific I might be doing wrong in the mapping file? Or do you just think its a case of them potentially being over engineered? Thanks for your help.