NHibernate Has-Many Collection With Cascading Deletes is Failing

Question

Objective:
Create a parent-child relationship such that modifications to the parent's list of children will propagate to all of the children and have NHibernate do the heavy lifting. The parent-child relationship will be a Has-Many on a self referencing table.

Problem:
Any attempt at deleting the parent (the root) object causes exceptions instead of the expected behavior of deleting the child objects.

Versions of stuff I am using:
Microsoft SQL Server Management Studio Version 10.0.4064.0
FluentNHibernate Version 1.3
NHibernate Version 3.2.0.4

Below is the set of current class objects and table structure I am using to replicate this behavior.

---

// Entity
class Task
{
    ID { get; set; }    
    public virtual IList<Task> Children { get; set; }
    public virtual byte[] Version { get; protected set; }
    public virtual bool IsNew() { return ID <= 0; }

    public Task()
    {
        this.Children = new System.Collections.Generic.List<Task>();
    }
    // Other properties excluded for brevity
}

---

// Map
class TaskMap : ClassMap<Task>
{
    TaskMap()
    {
        Table("Task");

        Id(x => x.ID, "ID")
            .GeneratedBy.HiLo(
                "NH_HiLo", "NextHigh", "100",
                string.Format("TableName =     '{0}'", "Task"));

        HasMany<Task>(x => x.Children) 
            .KeyColumn("ParentTaskID")
            .Cascade.AllDeleteOrphan();

        // Other properties omitted for brevity

         Version(x => x.Version)
            .Not.Nullable()
            .Generated.Always()
            .Column("Version")
            .CustomSqlType("timestamp");
    }
}

---

// Repository Delete Method:
public virtual void Delete(Task value)
{
    // CurrentSession is an ISession object that is currently open
    using (var transaction = CurrentSession.BeginTransaction())
    {
        try
        {
            CurrentSession.Delete(value);
            transaction.Commit();
        }
        catch (Exception)
        {
            transaction.Rollback();
            throw;
        }
    }
}

---

// Test Case using NUnit.Framework and FluentNHibernate.Testing:
[TestFixtureSetUp]
public void SetUpFixture()
{
    _repository = new Repository();
}

[Test]
public void MappingTest()
{
    var task = new Task(); // Omitted assigning other properties for brevity

    var entity = new Task(); // Omitted assigning other properties for brevity
    entity.Children.Add(task);

    _entity = new PersistenceSpecification<Task>(_repository.CurrentSession)
        .VerifyTheMappings(entity);
}                       

[TearDown]
public void TearDown()
{
    if (_entity != null && !_entity.IsNew())
    {
        _repository.Delete(_entity);
        _entity = null;
    }
}

---

--Table Script:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
CREATE TABLE [dbo].[Task](
    [ID] [bigint] NOT NULL,
    [ParentTaskID] [bigint] NULL, -- Notice it DOES HAVE a NULLable FK     reference.
    [Version] [timestamp] NOT NULL,
    CONSTRAINT [PK_MyTable] PRIMARY KEY CLUSTERED(
        [ID] ASC
    ) WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF,
        IGNORE_DUP_KEY = OFF,     ALLOW_ROW_LOCKS  = ON,
        ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO
ALTER TABLE [dbo].[Task]  WITH CHECK ADD  CONSTRAINT [FK_TasksChild_TasksParent]
    FOREIGN KEY([ParentTaskID])
    REFERENCES [dbo].[Task] ([ID]) -- Notice the self table reference for child objects
GO
ALTER TABLE [dbo].[Task] CHECK CONSTRAINT [FK_TasksChild_TasksParent]
GO

---

With the above table and classes, changing the cascade to these options and executing the specified during the teardown of the test, these are the results.

---

With Cascade.AllDeleteOrphan:
Simply calling delete on the parent object I get this exception:

NHibernate.StaleObjectStateException was unhandled by user code
Message=Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [Task#1015859]
Source=NHibernate
EntityName=Entities.Task
StackTrace:
   at NHibernate.Persister.Entity.AbstractEntityPersister.Check(Int32 rows, Object id, Int32 tableNumber, IExpectation expectation, IDbCommand statement) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs:line 2178
   at NHibernate.Persister.Entity.AbstractEntityPersister.Delete(Object id, Object version, Int32 j, Object obj, SqlCommandInfo sql, ISessionImplementor session, Object[] loadedState) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs:line 2912
   at NHibernate.Persister.Entity.AbstractEntityPersister.Delete(Object id, Object version, Object obj, ISessionImplementor session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs:line 3095
   at NHibernate.Action.EntityDeleteAction.Execute() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Action\EntityDeleteAction.cs:line 70
   at NHibernate.Engine.ActionQueue.Execute(IExecutable executable) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\ActionQueue.cs:line 136
   at NHibernate.Engine.ActionQueue.ExecuteActions(IList list) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\ActionQueue.cs:line 126
   at NHibernate.Engine.ActionQueue.ExecuteActions() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\ActionQueue.cs:line 174
   at NHibernate.Event.Default.AbstractFlushingEventListener.PerformExecutions(IEventSource session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs:line 249
   at NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultFlushEventListener.cs:line 19
   at NHibernate.Impl.SessionImpl.Flush() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 1489
   at NHibernate.Transaction.AdoTransaction.Commit() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Transaction\AdoTransaction.cs:line 190
   at Repositories.Repository.Delete(Task value) in ..\Repositories\Repository.cs:line 22
   at TaskTest.TearDown() in ..\Tests\TaskTest.cs:line 76

---

After iterating through each of the children, recursively digging through those children's children and attempting to delete each child from the bottom up:

NHibernate.ObjectDeletedException was unhandled by user code
Message=deleted object would be re-saved by cascade (remove deleted object from associations)[Task#1016061]
Source=NHibernate
EntityName=Entities.Task
StackTrace:
   at NHibernate.Impl.SessionImpl.ForceFlush(EntityEntry entityEntry) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 914
   at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.EntityIsTransient(SaveOrUpdateEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultSaveOrUpdateEventListener.cs:line 140
   at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.PerformSaveOrUpdate(SaveOrUpdateEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultSaveOrUpdateEventListener.cs:line 76
   at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.OnSaveOrUpdate(SaveOrUpdateEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultSaveOrUpdateEventListener.cs:line 53
   at NHibernate.Impl.SessionImpl.FireSaveOrUpdate(SaveOrUpdateEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 2662
   at NHibernate.Impl.SessionImpl.SaveOrUpdate(String entityName, Object obj) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 549
   at NHibernate.Engine.CascadingAction.SaveUpdateCascadingAction.Cascade(IEventSource session, Object child, String entityName, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\CascadingAction.cs:line 249
   at NHibernate.Engine.Cascade.CascadeToOne(Object parent, Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 216
   at NHibernate.Engine.Cascade.CascadeAssociation(Object parent, Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 181
   at NHibernate.Engine.Cascade.CascadeProperty(Object parent, Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 148
   at NHibernate.Engine.Cascade.CascadeCollectionElements(Object parent, Object child, CollectionType collectionType, CascadeStyle style, IType elemType, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 240
   at NHibernate.Engine.Cascade.CascadeCollection(Object parent, Object child, CascadeStyle style, Object anything, CollectionType type) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 201
   at NHibernate.Engine.Cascade.CascadeAssociation(Object parent, Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 185
   at NHibernate.Engine.Cascade.CascadeProperty(Object parent, Object child, IType type, CascadeStyle style, Object anything, Boolean isCascadeDeleteEnabled) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 148
   at NHibernate.Engine.Cascade.CascadeOn(IEntityPersister persister, Object parent, Object     anything) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\Cascade.cs:line 126
   at NHibernate.Event.Default.AbstractFlushingEventListener.CascadeOnFlush(IEventSource session, IEntityPersister persister, Object key, Object anything) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs:line 207
   at NHibernate.Event.Default.AbstractFlushingEventListener.PrepareEntityFlushes(IEventSource session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs:line 197
   at NHibernate.Event.Default.AbstractFlushingEventListener.FlushEverythingToExecutions(FlushEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs:line 48
   at NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultFlushEventListener.cs:line 18
   at NHibernate.Impl.SessionImpl.Flush() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 1489
   at NHibernate.Transaction.AdoTransaction.Commit() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Transaction\AdoTransaction.cs:line 190
   at Repositories.Repository.Delete(Task value) in ..\Repositories\Repository.cs:line 22
   at Repositories.Repository.Delete(Task value) in ..\Repositories\Repository.cs:line 25
   at Repositories.Repository.Delete(Task value) in ..\Repositories\Repository.cs:line 25
   at Tests.TaskTest.TearDown() in ..\Tests\TaskTest.cs:line 76

---

After iterating through the children, clearing each of their sets of children, then saving/deleting the parent I get this exception:

NHibernate.StaleObjectStateException was unhandled by user code
Message=Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect): [Task#1015960]
Source=NHibernate
EntityName=Entities.Task
StackTrace:
   at NHibernate.Persister.Entity.AbstractEntityPersister.Check(Int32 rows, Object id, Int32 tableNumber, IExpectation expectation, IDbCommand statement) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs:line 2178
   at NHibernate.Persister.Entity.AbstractEntityPersister.Delete(Object id, Object version, Int32 j, Object obj, SqlCommandInfo sql, ISessionImplementor session, Object[] loadedState) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs:line 2912
   at NHibernate.Persister.Entity.AbstractEntityPersister.Delete(Object id, Object version, Object obj, ISessionImplementor session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Persister\Entity\AbstractEntityPersister.cs:line 3095
   at NHibernate.Action.EntityDeleteAction.Execute() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Action\EntityDeleteAction.cs:line 70
   at NHibernate.Engine.ActionQueue.Execute(IExecutable executable) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\ActionQueue.cs:line 136
   at NHibernate.Engine.ActionQueue.ExecuteActions(IList list) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\ActionQueue.cs:line 126
   at NHibernate.Engine.ActionQueue.ExecuteActions() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Engine\ActionQueue.cs:line 174
   at NHibernate.Event.Default.AbstractFlushingEventListener.PerformExecutions(IEventSource session) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\AbstractFlushingEventListener.cs:line 249
   at NHibernate.Event.Default.DefaultFlushEventListener.OnFlush(FlushEvent event) in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Event\Default\DefaultFlushEventListener.cs:line 19
   at NHibernate.Impl.SessionImpl.Flush() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Impl\SessionImpl.cs:line 1489
   at NHibernate.Transaction.AdoTransaction.Commit() in d:\CSharp\NH\NH\nhibernate\src\NHibernate\Transaction\AdoTransaction.cs:line 190
   at Repositories.Repository.Delete(Task value) in ..\Repositories\Repository.cs:line 22
   at TaskTest.TearDown() in ..\Tests\TaskTest.cs:line 76

---

With Cascade.All, simply calling delete on the parent object I get this exception:
Same as for Cascade.AllDeleteOrphan

After iterating through each of the children, recursively digging through those children's children and attempting to delete each child from the bottom up:
Same as for Cascade.AllDeleteOrphan

After iterating through the children, clearing each of their sets of children, then saving/deleting the parent I get this exception:
No exception: The parent gets deleted correctly but now I have orphaned objects that I do not want!

---

I have the looked through many blogs/stackoverflow questions/resource docs and have not really seen a solution to this issue.
Here are a few of the links I have dug through already:

• How to delete a referenced object using FluentNHibernate (ye olde "deleted object would be resaved by cascade")
• Error in Cascade : deleted object would be re-saved by cascade
• Setting up Fluent NHibernate one-to-many with cascading deletes using the automapper
• key-many-to-one and key-property association: nhibernate won't DELETE items from set
• https://nhibernate.jira.com/browse/NH-1050
  (notice I have the null FK)
• Row was updated or deleted by another transaction (or unsaved-value mapping was incorrect)
  (notice I use timestamp optimistic versioning)
• https://forum.hibernate.org/viewtopic.php?t=933496
  (comment by ernst_pluess about cascade=all threw a warning flag about using HiLo, but is HiLo generated or assigned? because technically NHibernate generates it then assigns it...)
• Exception deleting child records in NHibernate
  (makes it seem like I have to manually delete all child objects, which takes away the purpose of having cascade!!)

---

Many of the posts mention inverting the relationship but setting .inverse and making the child own the relationship is totally not the goal here!

I have no idea what I am missing but hopefully this is something really simple to fix that I am overlooking. Any help will be much appreciated!

Alfi

Answer 1

You are not missing anything. It is a combination of your mapping: a) child does not have a Parent mapped, b) child is versioned, c) collection is not set as inverse (because it cannot be managed by child without mapped parent) d) and finally, most likely due to a bug.

What happens, is that with versioning, any INSERT or UPDATE statement is followed by SELECT... to get the latest timestamp generated by DB Server. But this does not happen in one case:

1. Collection parent is inserted
2. parent version selected from DB
3. child inserted
4. child version selected from DB
5. child updated (no inversion) to reference parent
   • -- NOTHING - child version IS NOT selected...

Because the child version after the relation update is different then the one just incremented in DB... later the StaleException is thrown.

The best you can do is extend the mapping to have a Parent... and make it inverse

Cleanser

I appreciate your reply. This wasn't exactly what I was hoping to hear though as I was hoping I didn't have to manually break the relationship between parent and child but it looks like it is unavoidable. I did get the test to pass by adding a ParentTask reference and tweaking the delete method to recursively dig down through the child lists setting the parent to null to break the tie and finally delete the parent task which, when Cascade.AllDeleteOrphan is on, correctly deletes all of the orphaned tasks. Again, thank you for your reply. – Alfi