NH-2901 - Multiple .Fetch() calls within Future query results in collection that does not persist deletes

[nhibernate-bot]

Richard Thorne created an issue — 28th September 2011, 17:45:42:

I have a "Game" entity that has a static method "GetFuture" which returns an IFutureValue<Game> provided by nHibernate, fairly standard stuff. I recently added an optional Func<IQueryOver<Game, Game>, IQueryOver<Game, Game>> parameter to allow for custom fetching strategies to be supplied to reduce roundtrips further. The code looks like this:

var gameFuture = Game.GetFuture(id, query =>
{
     query = query.Fetch(x => x.CompletedActivities).Eager;
                                                        
     if (someCondition)
     {
          query = query.Fetch(x => x.Items).Eager;
     }

     return query;
});

Later when I .Remove() an item from the "Items" collection, the delete is not issued to the database. However if I remove the second .Fetch() in the Func<> parameter so that .Items is lazily-loaded later, the delete is issued correctly. I'm unsure if this is a bug or I'm just doing things wrong. Here are the mapping snippets for the two items:

<class name="World.Game" table="Game">
    <cache usage="read-write" region="Short" />
    <id name="Id">
      <generator class="identity" />
    </id>
    
    <bag name="Items" inverse="true" cascade="all-delete-orphan" lazy="true" order-by="id ASC">
      <cache usage="read-write" region="Short" />
      <key column="game" />
      <one-to-many class="World.Entities.Entity" />
    </bag>
  </class>

  <class name="World.Entities.Entity" table="WorldContents">
    <cache usage="read-write" region="Short" />
    <id name="Id">
      <generator class="identity" />
    </id>
    <many-to-one name="Game" />
    <property name="X" />
    <property name="Y" />
  </class>

World.Entities.Entity has a number of joined subclasses.

I get the same problem when using the Linq .Query<T>() provider and when using the .QueryOver<T>() provider.

Using MySQL .NET Connector on .NET 4.

---

Richard Thorne added a comment — 28th September 2011, 17:50:51:

Oh I forgot to add, the GetFuture method body looks like this:

public IFutureValue<Game> GetFuture(int id, Func<IQueryOver<Game, Game>, IQueryOver<Game, Game>> modifier = null)
{
     IQueryOver<Game, Game> query = session.QueryOver<Game>().Where(x => x.Id == id);

     if (modifier != null)
     {
          query = modifier(query);
     }

     return query.FutureValue();
}

[fredericDelaporte]

Can you provide a test case? See contributing.

And please note that some analysis has been done on your ticket here:

Unclear ticket. He either tries to fetch multiple bags in one query which throws exception (maybe missing delete due to wrong exception handling?)
Or tries to fetch not mapped collection - which is no op and doesn't affect behavior in any way (double checked it).

[bahusoid]

So I believe it's not an issue.
We don't support fetching multiple bag collections in one DB roundtrip (and it's clear in example that multiple collections are fetched)
And in this case I believe Items bag + CompletedActivities set (missing in mapping) is fetched in one query and that leads to records duplication in Items bag. So when user tried to delete some record - it's not deleted as he deleted only one record and duplicate is left in collection. So solution - don't fetch multiple collections in one query.