[nhibernate-issues] [NHJIRA] Commented: (NH-2705) Linq/Hql/Criteria Fetch on class hierarchy generates invalid SQL when derivees mix component and many-to-one mappings

[Andrei A. (JIRA) <nh...@gm...>]

    [ http://216.121.112.228/browse/NH-2705?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=21092#action_21092 ] 

Andrei Alecu commented on NH-2705:
----------------------------------

Alright, then I guess the bug is that there's not a clear exception being thrown if this is not a supported scenario. :)

I believe we should get an exception instead of executing invalid SQL.

Regarding not being able to fetch through components, I believe that's also a bug, your comment:

  The LINQ 
session.Query<T>().Fetch(p => p.SubItem.Details).Where(p => p.SubItem.Name == name).ToList(); 
is NH-2615

Results in the following error:

  A fetch request must be a simple member access expression of the kind o => o.Related; 'p.SubItem.Details' is too complex.\r\nParameter name: relatedObjectSelector

So, there's no way to fetch through components currently.

> Linq/Hql/Criteria Fetch on class hierarchy generates invalid SQL when derivees mix component and many-to-one mappings
> ---------------------------------------------------------------------------------------------------------------------
>
>                 Key: NH-2705
>                 URL: http://216.121.112.228/browse/NH-2705
>             Project:  NHibernate
>          Issue Type: Improvement
>          Components: Core
>    Affects Versions: 3.1.0
>            Reporter: Andrei Alecu
>            Priority: Minor
>         Attachments: nh2705 test.patch
>
>
> Consider the following scenario:
>     public class ItemBase
>     {
>         public virtual int Id { get; set; }
>         public virtual SubItemBase SubItem { get; set; }
>     }
>     public class ItemWithComponentSubItem:ItemBase { }
>     
>     public class ItemWithManyToOneSubItem:ItemBase { }
> ItemWithComponentSubItem defines in its mapping that SubItem is a component of SubItemComponent type (which derives from SubItemBase)
> ItemWithManyToOneSubItem defines in its mapping that SubItem is a many-to-one of SubItemEntity type (again, derives from SubItemBase)
> Running the following query with fetch results in invalid SQL being executed:
>      from ItemBase i left join fetch i.SubItem
> Removing the fetch makes it work properly.
>      from ItemBase i
> Also, this works:
>      from ItemWithManyToOneSubItem i left join fetch i.SubItem
> But this doesn't:
>      from ItemWithComponentSubItem i left join fetch i.SubItem (one would argue there's nothing to fetch here, but instead of throwing an exception, the fetch instruction should just be ignored and maybe a warning logged, it would allow for much better reuse of code)
> I will attach a unit test that demonstrates this bug, and also a related one at NH-2615.
> I believe the correct behavior here is to allow fetch on components, and simply ignore it rather than throwing an exception.

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