nhibernate: why does nhibernate update the foreign key of my child entity?

Question

Ok, i have two entities named WorkPostSheet and WorkPost where the WorkPostSheet contains a collection of WorkPost-items:

public class WorkPostSheet
{
    ...

    public virtual IEnumerable<WorkPost> WorkPosts
    {
        get;
        private set;
    }
}

In my integration test, i notice that nhibernate creates an update statement which I cannot understand. The test:

    [Test]
    public void Commit_CreateNewWorkPostSheetWithWorkPosts_WorkPostsPersisted()
    {
        using (IUnitOfWork unitOfWork = IsolatingFactory.CreateReadOnlyUnitOfWork())
        {
            // arrange
            WorkPostSheetRepository repository = new WorkPostSheetRepository(IsolatingFactory);
            WorkItemRepository workItemRepository = new WorkItemRepository(IsolatingFactory);

            DateTime from = new DateTime(2000, 1, 1);
            DateTime to = new DateTime(2000, 2, 1);
            WorkPostSheet sheetWithWorkPosts = WorkPostSheet.Create(TestData.CreateAndCommitUser("min", "Marius", "Ingjer", IsolatingFactory), new TimePeriod(from, to));

            WorkItem workItemToPostWorkOn = WorkItem.Create(0, "A");
            workItemRepository.Commit(workItemToPostWorkOn);

            WorkPost workPost = sheetWithWorkPosts.Add(workItemToPostWorkOn, from);

            // act
            repository.Commit(sheetWithWorkPosts);
            unitOfWork.Session.Flush();
            unitOfWork.Session.Clear();

            WorkPostSheet sheetWithWorkPostsFromDb = repository.Get(sheetWithWorkPosts.Id, false);

            // assert
            CollectionAssert.Contains(sheetWithWorkPostsFromDb.WorkPosts, workPost);
        }
    }

The output:

NHibernate: INSERT INTO "User" (UserName, FirstName, LastName) VALUES (@p0, @p1, @p2); select last_insert_rowid();@p0 = 'min', @p1 = 'Marius', @p2 = 'Ingjer'

This makes sence since I am creating a user (TestData.CreateAndCommitUser)

NHibernate: INSERT INTO "WorkItem" (LastChanged, Description, Id) VALUES (@p0, @p1, @p2);@p0 = 06.01.2010 21:50:25, @p1 = 'A', @p2 = 0

This makes sence since I am creating a workitem

NHibernate: INSERT INTO "WorkPostSheet" (PeriodFrom, PeriodTo, userId) VALUES (@p0, @p1, @p2); select last_insert_rowid();@p0 = 01.01.2000 00:00:00, @p1 = 01.02.2000 00:00:00, @p2 = 1

This makes sence as I am creating a workpost sheet

NHibernate: INSERT INTO "WorkPost" (WorkDone, workItemId, sheetId) VALUES (@p0, @p1, @p2); select last_insert_rowid();@p0 = 0, @p1 = 0, @p2 = 1

This is commited in the WorkPostRepository (workpost sheet is root entity)

NHibernate: UPDATE "WorkPost" SET sheetId = @p0 WHERE Id = @p1;@p0 = 1, @p1 = 1

Now this one I not understand. The foreign is updated with the same value assigned when the entity was first commited. Can you help me understand this?

NHibernate: SELECT workpostsh0_.Id as Id3_1_, workpostsh0_.PeriodFrom as PeriodFrom3_1_, workpostsh0_.PeriodTo as PeriodTo3_1_, workpostsh0_.userId as userId3_1_, user1_.Id as Id0_0_, user1_.UserName as UserName0_0_, user1_.FirstName as FirstName0_0_, user1_.LastName as LastName0_0_ FROM "WorkPostSheet" workpostsh0_ inner join "User" user1_ on workpostsh0_.userId=user1_.Id WHERE workpostsh0_.Id=@p0;@p0 = 1

Load from repository

NHibernate: SELECT workposts0_.sheetId as sheetId2_, workposts0_.Id as Id2_, workposts0_.Id as Id2_1_, workposts0_.WorkDone as WorkDone2_1_, workposts0_.workItemId as workItemId2_1_, workposts0_.sheetId as sheetId2_1_, workitem1_.Id as Id1_0_, workitem1_.LastChanged as LastChan2_1_0_, workitem1_.Description as Descript3_1_0_ FROM "WorkPost" workposts0_ inner join "WorkItem" workitem1_ on workposts0_.workItemId=workitem1_.Id WHERE workposts0_.sheetId=@p0;@p0 = 1

Lazy load

Here are the mapping files:

sealed class WorkPostClassMap : ClassMap<WorkPost>
{
    public WorkPostClassMap()
    {
        Not.LazyLoad();

        Id(post => post.Id).GeneratedBy.Identity().UnsavedValue(0);
        Map(post => post.WorkDone);
        References(post => post.Item).Column("workItemId").Not.Nullable();
        References(Reveal.Property<WorkPost, WorkPostSheet>("Owner"), "sheetId").Not.Nullable();
    }
}

sealed class WorkPostSheetClassMap : ClassMap<WorkPostSheet>
{
    public WorkPostSheetClassMap()
    {
        Id(sheet => sheet.Id).GeneratedBy.Identity().UnsavedValue(0);
        Component(sheet => sheet.Period, period =>
                                             {
                                                 period.Map(p => p.From, "PeriodFrom");
                                                 period.Map(p => p.To, "PeriodTo");
                                             });
        References(sheet => sheet.Owner, "userId").Not.Nullable();
        HasMany(sheet => sheet.WorkPosts).KeyColumn("sheetId").AsBag();
    }
}

Answer 1

Did you set the "inverse" attribute to "true" for the collection side of the association?

See: http://ayende.com/Blog/archive/2009/01/18/nh-prof-new-feature-superfluous-ltmany-to-onegt-update.aspx