[nhibernate-issues] [NHJIRA] Commented: (NH-2784) NHibernate does extra select on each missing relations, even using an eager fetching.

[Julian M. (JIRA) <nh...@gm...>]

    [ http://216.121.112.228/browse/NH-2784?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=21348#action_21348 ] 

Julian Maughan commented on NH-2784:
------------------------------------

I had a look at your FNH mappings. I don't really known FNH, but it looks correct. Having said that I was unable to reproduce the problem using a ByCode mapping:

mapper.Class<Order>(m =>
{
	m.Table("`Order`");
	m.Id(x => x.Id, map => map.Generator(Generators.Assigned));
	m.Property(model => model.Name);
	m.ManyToOne<User>(model => model.User, map => map.Column("TheUser"));
});

mapper.Class<User>(m =>
{
	m.Table("`User`");
	m.Id(x => x.Id, map => map.Generator(Generators.Assigned));
	m.Property(model => model.Name);
});

Are you saying that both SELECT statements are executed by the Criteria query, or is the second one only executed later on when you access the Order with ID = 3?

> NHibernate does extra select on each missing relations, even using an eager fetching.
> -------------------------------------------------------------------------------------
>
>                 Key: NH-2784
>                 URL: http://216.121.112.228/browse/NH-2784
>             Project:  NHibernate
>          Issue Type: Bug
>          Components: Core
>    Affects Versions: 3.1.0
>            Reporter: Peter Kiers
>
> When I do an eager join on a relation table, whenever the relation is missing it will generate an additional query for each missing relation.
> Table layout / data:
> TableName: Order
> +----+-----------+--------+
> | Id | OrderName | UserId |
> +----+-----------+--------+
> | 1  | OrderA    | 1      |
> | 2  | OrderB    | 2      |
> | 3  | OrderC    | 3      |  
> +-------------------------+  
> TableName: User
> +----+-----------+
> | Id | UserName  |
> +----+-----------+
> | 1  | User1     |
> | 2  | User2     |
> +----------------+
> var orders = session.CreateCriteria<Order>().SetFetchMode("User", 
> FetchMode.Eager).List<Order>(); 
> Console output:
> NHibernate: SELECT this_.Id as Id0_1_, this_.OrderName as OrderName0_1_, this_.User_id as User3_0_1_, user2_.Id as Id1_0_, user2_.UserName as UserName1_0_ FROM[Order] this_ left outer join [User] user2_ on this_.User_id=user2_.Id
> NHibernate: SELECT user0_.Id as Id1_0_, user0_.UserName as UserName1_0_ FROM [User] user0_ WHERE user0_.Id=@p0;@p0 = 3 [Type: Int32 (0)]
> As you can see it tries to get UserID 3 (which doesn't exists) but it should already know it isn't there as I did a eager fetchmode on that table.

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