Many-To-Many and cascades: Problem with entities deletion

Question

I have the following two entities, with their mappings:

public class VideoCategory : BaseEntity<VideoCategory>
{
    private readonly Iesi.Collections.Generic.ISet<VideoFolder> folders = new HashedSet<VideoFolder>();

    public VideoCategory()
    {

    }

    public VideoCategory(string name)
    {
        Name = name;
    }

    public string Name { get; set; }


    public IEnumerable<VideoFolder> Folders { get { return folders; } }

    public void AddFolder(VideoFolder videoFolder)
    {
        Contract.Requires(videoFolder != null);

        if (folders.Contains(videoFolder))
            return;

        folders.Add(videoFolder);
        videoFolder.AddCategory(this);
    }

    public void RemoveFolder(VideoFolder videoFolder)
    {
        folders.Remove(videoFolder);
        videoFolder.RemoveCategory(this);
    }

    public void ClearFolders()
    {
        folders.ForEach(f => f.RemoveCategory(this));

        folders.Clear();
    }
}

public class VideoFolder : BaseEntity<VideoFolder>
{
    private readonly Iesi.Collections.Generic.ISet<VideoCategory> categories = new HashedSet<VideoCategory>();

    public VideoFolder()
    {

    }

    public VideoFolder(string path)
    {
        Path = path;
    }

    public string Path { get; set; }
    public string Name { get; private set; }

    public IEnumerable<VideoCategory> Categories { get { return categories; } }

    protected internal void AddCategory(VideoCategory videoCategory)
    {
        Contract.Requires(videoCategory != null);

        categories.Add(videoCategory);
    }

    protected internal void RemoveCategory(VideoCategory videoCategory)
    {
        categories.Remove(videoCategory);
    }
}

public class VideoCategoryMap : ClassMap<VideoCategory>
{
    public VideoCategoryMap()
    {
        Table("VideoCategories");

        Id(cat => cat.Id)
            .GeneratedBy.Native();

        Map(cat => cat.Name)
            .Unique()
            .Not.Nullable();

        HasManyToMany<VideoFolder>(Reveal.Member<VideoCategory>("folders"))
            .Access.CamelCaseField()
            .AsSet()
            .Inverse()
            .Cascade.AllDeleteOrphan();
    }
}

public class VideoFolderMap : ClassMap<VideoFolder>
{
    public VideoFolderMap()
    {
        Table("VideoFolders");

        Id(folder => folder.Id)
            .GeneratedBy.Native();

        Map(folder => folder.Path)
            .Not.Nullable();

        HasManyToMany<VideoCategory>(Reveal.Member<VideoFolder>("categories"))
            .Access.CamelCaseField()
            .AsSet();
    }
}

I have these 2 unit-tests:

[Fact]
public void DeletingVideocategory_DeletesVideoFolders()
{
    object id;

    using (ISession session = SessionFactory.OpenSession())
    {
        var categ = new VideoCategory("Foo");
        var folder = new VideoFolder("D:\\Foo");
        categ.AddFolder(folder);

        id = session.Save(categ);

        session.Flush();
    }

    using (ISession session = SessionFactory.OpenSession())
    {
        var category = session.Get<VideoCategory>(id);
        category.ClearFolders();

        session.Delete(category);
        session.Flush();

        Assert.Equal(0, session.QueryOver<VideoFolder>().RowCount());
    }
}

[Fact]
public void DeletingVideocategory_DoesntDeleteVideoFoldersOwned_ByOtherCategories()
{
    object id;
    object id2;

    using (ISession session = SessionFactory.OpenSession())
    {
        var categ = new VideoCategory("Foo");
        var categ2 = new VideoCategory("Bar");
        var folder = new VideoFolder("D:\\Foo");

        categ.AddFolder(folder);
        categ2.AddFolder(folder);

        id = session.Save(categ);
        id2 = session.Save(categ2);

        session.Flush();
    }

    using (ISession session = SessionFactory.OpenSession())
    {
        var category = session.Get<VideoCategory>(id);
        category.ClearFolders();

        session.Delete(category);
        session.Flush();

        Assert.Equal(1, session.QueryOver<VideoFolder>().RowCount());
        Assert.Equal(1, session.Get<VideoCategory>(id2).Folders.Count());
    }
}

The first one succeeds, but not the first Assert of the second, where the video folder is deleted, whereas it is still associated with the remaining video category.

Here is the SQL output of the second test:

INSERT INTO VideoCategories (Name) VALUES (@p0); select last_insert_rowid();@p0 = 'Foo' [Type: String (0)]
INSERT INTO VideoFolders (Path) VALUES (@p0); select last_insert_rowid();@p0 = 'D:\Foo' [Type: String (0)]
INSERT INTO VideoCategories (Name) VALUES (@p0); select last_insert_rowid();@p0 = 'Bar' [Type: String (0)]
INSERT INTO CategoriesToFolders (VideoFolder_id, VideoCategory_id) VALUES (@p0, @p1);@p0 = 1 [Type: Int32 (0)], @p1 = 1 [Type: Int32 (0)]
INSERT INTO CategoriesToFolders (VideoFolder_id, VideoCategory_id) VALUES (@p0, @p1);@p0 = 1 [Type: Int32 (0)], @p1 = 2 [Type: Int32 (0)]
SELECT videocateg0_.Id as Id10_0_, videocateg0_.Name as Name10_0_ FROM VideoCategories videocateg0_ WHERE videocateg0_.Id=@p0;@p0 = 1 [Type: Int32 (0)]
SELECT folders0_.VideoCategory_id as VideoCat1_1_, folders0_.VideoFolder_id as VideoFol2_1_, videofolde1_.Id as Id13_0_, videofolde1_.Path as Path13_0_ FROM CategoriesToFolders folders0_ left outer join VideoFolders videofolde1_ on folders0_.VideoFolder_id=videofolde1_.Id WHERE folders0_.VideoCategory_id=@p0;@p0 = 1 [Type: Int32 (0)]
SELECT categories0_.VideoFolder_id as VideoFol2_1_, categories0_.VideoCategory_id as VideoCat1_1_, videocateg1_.Id as Id10_0_, videocateg1_.Name as Name10_0_ FROM CategoriesToFolders categories0_ left outer join VideoCategories videocateg1_ on categories0_.VideoCategory_id=videocateg1_.Id WHERE categories0_.VideoFolder_id=@p0;@p0 = 1 [Type: Int32 (0)]
SELECT videos0_.VideoFolder_id as VideoFol3_1_, videos0_.Id as Id1_, videos0_.Id as Id12_0_, videos0_.Path as Path12_0_ FROM VideoFiles videos0_ WHERE videos0_.VideoFolder_id=@p0;@p0 = 1 [Type: Int32 (0)]
DELETE FROM CategoriesToFolders WHERE VideoFolder_id = @p0;@p0 = 1 [Type: Int32 (0)]
DELETE FROM VideoFolders WHERE Id = @p0;@p0 = 1 [Type: Int32 (0)]
DELETE FROM VideoCategories WHERE Id = @p0;@p0 = 1 [Type: Int32 (0)]
SELECT count(*) as y0_ FROM VideoFolders this_

If I change the mapping, and modify Cascade.AllDeleteOrphan in VideoCategoryMap, the second test succeeds, whereas the first fails, because the orphaned video folder isn't deleted.

How can I make both tests to succeed?

Thanks in advance

Mike

Answer 1

"Delete orphan" in NHibernate doesn't mean "Delete entities without any other parents". It means "when deleting the relationship, delete the referenced entity too".

NHibernate doesn't handle the case that you need OOTB. Possible solutions include domain-level logic, repository-level logic, event listeners and triggers.