[nhibernate-issues] [NHJIRA] Commented: (NH-2500) NH 3.0 Linq provider uses query parameters from first call in subsequent calls.

[Patrick E. (JIRA) <nh...@gm...>]

    [ http://216.121.112.228/browse/NH-2500?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=20505#action_20505 ] 

Patrick Earl commented on NH-2500:
----------------------------------

Hi Nicola.  I looked through your patch and have a couple questions.

1.  Have you considered what might happen with subqueries?  I'm still learning about the code myself, but I saw some indication that subqueries also use the result transformer, and I'm not sure if the current code covers those cases.  I came up with this thought after looking to see if the ResultTransformer constructor could be called with the list of constants, instead of setting it directly as a property.

2.  It seems like the ExpressionKeyVisitor would also need to be adjusted.  Did you or could you look into this as well?

3.  As a random thought, it would be good if NHibernate didn't maintain references to the external objects in any query/expression cache so things can be garbage collected properly.

Thanks so much for the work you put into the patch!

> NH 3.0 Linq provider uses query parameters from first call in subsequent calls.
> -------------------------------------------------------------------------------
>
>                 Key: NH-2500
>                 URL: http://216.121.112.228/browse/NH-2500
>             Project:  NHibernate
>          Issue Type: Bug
>          Components: Linq Provider
>    Affects Versions: 3.0.0.GA
>            Reporter: Andrey Titov
>            Assignee: Patrick Earl
>            Priority: Critical
>         Attachments: NH-2500.patch, NHTest3.zip
>
>
> NH 3.0 Linq provider uses query parameters from first call in subsequent calls if this parameters are not propagated to SQL.
> //in first session
> this.number = 545;
> var cats = session.Query<Cat>().Select(cat => new CatInfo { Name = cat.Name, SomeNumber = this.number }).ToList();
> // all works perfect: all CatInfos contains 545
> //later in another session
> this.number = 842;
> var cats = session.Query<Cat>().Select(cat => new CatInfo { Name = cat.Name, SomeNumber = this.number }).ToList();
> // magic happens: all CatInfos contains 545 again
> I've debugged NH and found that in second query it gets QueryPlan from cache in NHibernate.Impl.AbstractSessionImpl.GetHQLQueryPlan() and it contains parameters from first call of query (NHibernate.Linq.NhLinqExpression.ParameterValuesByName) and then fails to replace them in NHibernate.Linq.NhQueryProvider.SetParameters() because they are not actual SQL parameters (query.NamedParameters).
> Sample solution is attached (VS2010, SQL Server Express DB). Put NH and LinFu.DynamicProxy binaries to .Libraries\NHibernate before build.
> I think actual parameters should be cleared from query (set to default(T)) before putting plan in QueryPlanCache to let them be garbage collected and prevent real magic happen in case of similar bugs.

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