What’s the frequency, Kenneth?

Posted 1.13.08 in Uncategorized

In our latest project, our team made use of NHibernate to act as an ORM (Object-Relational Mapper) and to handle all of our data access work.

In the current phase that we are working on, we’re running into a problem. We can’t get NHibernate to delete a child object in a collection on a parent.

Here’s the basic situation:

We have a Proposal, which has a collection of ProposalMilestones. The ProposalMilestone has a reference to the parent Proposal, as well as a reference to the Milestone that it refers to.

When trying to remove a ProposalMilestone from the collection and flushing the session, NHibernate throws a StaleObjectException.

Here are images of the class diagram for this section and the database schema that applies:

 

Nothing special about either one. The relationships are as would be expected. 

Here are the related mapping files:

Proposal.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="CIV.Entities" assembly="NHSample" default-access="nosetter.camelcase" default-lazy="false">
    <class name="CIV.Entities.Proposal, NHSample" table="Proposal">
        <id name="Id" column="ID">
            <generator class="guid.comb" />
        </id>
        <version name="Version" column="Version" type="CIV.Entities.Timestamp, NHSample" generated="always" />
        <component name="Audit" class="CIV.Entities.Audit, NHSample">
            <property name="CreatedBy" column="CreatedBy"/>
            <property name="CreatedOn" column="CreatedOn" />
            <property name="ModifiedBy" column="ModifiedBy" />
            <property name="ModifiedOn" column="ModifiedOn" />
        </component>

        <property name="Code" column="Code" />
        <property name="Description" column="Description" />
        <property name="Name" column="Name" />
        <property name="ProposedStartDate" column="ProposedStartDate" />

        <bag name="Milestones" table="ProposalMilestone" inverse="true" cascade="all">
            <key column="ProposalID" />
            <one-to-many class="CIV.Entities.ProposalMilestone, NHSample" />
        </bag>
    </class>
</hibernate-mapping>

ProposalMilestone.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="CIV.Entities" assembly="NHSample" default-access="nosetter.camelcase" default-lazy="false">
    <class name="CIV.Entities.ProposalMilestone" table="ProposalMilestone">
        <id name="Id" column="ID" unsaved-value="00000000-0000-0000-0000-000000000000">
            <generator class="guid.comb" />
        </id>
        <version name="Version" column="Version" type="CIV.Entities.Timestamp, NHSample" generated="always" />
        <component name="Audit" class="CIV.Entities.Audit, NHSample">
            <property name="CreatedBy" column="CreatedBy"/>
            <property name="CreatedOn" column="CreatedOn" />
            <property name="ModifiedBy" column="ModifiedBy" />
            <property name="ModifiedOn" column="ModifiedOn" />
        </component>
        <property name="OriginalDueDate" column="OriginalDueDate" type="DateTime" />
        <many-to-one name="Milestone" column="MilestoneID" class="CIV.Entities.Milestone, NHSample"/>
        <many-to-one name="Proposal" column="ProposalID" not-null="true" class="CIV.Entities.Proposal, NHSample" />
        <bag name="Notifications" inverse="true" cascade="all">
            <key column="ProposalMilestoneID" />
            <one-to-many class="CIV.Entities.Notification, NHSample" />
        </bag>
    </class>
</hibernate-mapping>

Milestone

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" assembly="NHSample"  namespace="CIV.Entities" default-access="nosetter.camelcase" default-lazy="false">
    <class name="CIV.Entities.Milestone, NHSample" table="Milestone">
        <id name="Id" column="ID">
            <generator class="guid.comb"/>
        </id>
        <version name="Version" column="Version" type="CIV.Entities.Timestamp, NHSample" generated="always" />
        <component name="Audit" class="CIV.Entities.Audit, NHSample">
            <property name="CreatedBy" column="CreatedBy" type="String" />
            <property name="CreatedOn" column="CreatedOn" type="DateTime" />
            <property name="ModifiedBy" column="ModifiedBy" type="String" />
            <property name="ModifiedOn" column="ModifiedOn" type="DateTime" />
        </component>
        <property name="Name" column="Name" type="String" not-null="true" />
        <property name="Code" column="Code" type="String" not-null="true" />
        <property name="Description" column="Description" type="String" />

    </class>
</hibernate-mapping>

Any suggestions would be greatly appreciated.

As a side note, I think my relations expressed in the mapping could be better. ProposalMilestone is being treated as an entity right now, but there is no reason (unless NHibernate requires it for the relationships) that it needs to be. I believe Milestone is a value object, but again, it’s being treated as an entity.

Suggestions here would also be appreciated.

Updated (3.29.08)

I did get this problem solved: The final thing that worked for me was putting the optimistic-lock=”false” tag on the collection declaration (Proposal). This avoided updating the Proposal before the collection of ProposalMilestones was updated, which was causing my stale object error.

3 Responses to “Problems With NHibernate”

1. Brendan Says:
   January 14th, 2008 at 5:51 pm

   Hi Mate, One thing you might need to read up on is how collections and inverse collections are handled by NHibernate.

   I’m going to have a stab in the dark, but maybe this will help: For your ProposalMilestone to be deleted you might have to delete it from the collection and then delete the ProposalMilestone itself before you call flush. This is because you have a bi-directional relationship between ProposalMilestone and Proposal. When this is the case you need to delete both sides of the relationship for NHibernate to figure out it’s supposed to be deleted.

2. brendan Says:
   January 15th, 2008 at 2:32 pm

   i take it that wasn’t the problem then? oh well, good luck to you…

3. freqken Says:
   January 17th, 2008 at 10:27 pm

   Brendan,

   that was part of the problem. The final thing that worked for me was putting the optimistic-lock=”false” tag on the collection declaration (Proposal). This avoided updating the Proposal before the collection of ProposalMilestones was updated, which was causing my stale object error.

   I had missed that tag in all my trips through the docs, until I was specifically reading for each and every tag on a bag, set, etc.

   Thanks for the help and suggestion

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