I'm trying to create a standard parent-child relationship, code:



mapping in ChangeRequestItem.hbm.xml:

<bag generic="true" name="FurtherComments" cascade="all-delete-orphan" access="field.pascalcase-m-underscore">
<key column="ChangeRequestItemId" />
<one-to-many class="FB.CRS.Core.FurtherComment, FB.CRS.Core" />
</bag>

As can be seen the relationship is uni-directional from the ChangeRequestItem object, however I run into an issue when adding the FurtherComment object to the ChangeRequestItem whereby the foreign key value is not being inserted into the FurtherComment's table, so I get the following exception:

Cannot insert the value NULL into column 'ChangeRequestItemId', table 'CRS.dbo.CRSFurtherComment'; column does not allow nulls. INSERT fails.
The statement has been terminated.

After some digging I found the following on stackoverflow http://stackoverflow.com/questions/5558 ... ny-problem which appears to be the same issue, in the answers section he solves it by making the relationship bi-directional, is this really the only way? I don't really want to have the bi-directional relationhip as it makes no sense in the domain model.

Any help is appreciated.

Thanks,
Mike

I have the same issue posted on another thread and have yet to get a response that solves the issue but I did locate a post that does explain a possible "fix"

Posted: Fri Mar 20, 2009 7:06 pm Post subject:

http://bchavez.bitarmory.com/archive/20 ... ibute.aspx


In the unidirectional case, the foreign key column in the child table doesn't map to a property in the child object; it is in the data model, but not the object model. Since it is unidirectional there is just a property in the parent object [that contains a collection of children]; not the child [the child object does not contain any information back to the parent]. In addition, because Hibernate will first insert the child row (with a NULL foreign key) and then update it [the inserted row] later [with the parent's primary key].


I found this post explaining what I wish to accomplish and was a bit put put off by the statement "In addition, the foreign key column[in the child table] has to be defined as nullable because Hibernate will first insert the child row". From a DBA perspective this is a huge no-no and in most companies would not be accepted.

Thanks for the reply, that's a really good article and explains the issue well, in the end I went for the nullable foreign key as I have full control over the DB.

My understanding seems that there is a trade off were you either accept the nullable foreign key and keep it uni-directional or change the domain to be be bi-directional and make the child responsible for setting the relationship.