Sorry Manish and all, there is a small error in the above code.
The 3rd line:
var query = Linq<Person>("person").Where( predicate );
Is not correct, Somehow I deleted the "Session." part in there.
Correct is:
var query = Session.Linq<Person>("person").Where( predicate );
The test function after correction:
private void Test( Expression<Func<Person, bool>> predicate )
{
var query = Session.Linq<Person>("person").Where( predicate );
var resultList = query.ToList();
Assert.That(resultList,
Has.All.AssignableTo(typeof(Person)));
}
Sorry for that..
*Mohamed Meligy
*Readify | Senior Developer
M:*+61 451 835006* | W: www.readify.net
[image: Description: Description: Description: Description:
rss_16]<http://gurustop.net/>
[image: Description: Description: Description: Description:
cid:[email protected]]
<http://www.linkedin.com/in/meligy> [image:
Description: Description: Description: Description:
cid:[email protected]] <http://twitter.com/meligy>
On Thu, Sep 23, 2010 at 12:35 AM, Mohamed Meligy <[email protected]>wrote:
> @Manish.
> Let's say that Expression is the text that represents the function, and
> func is the function you get when you compile that text (over
> simplification).
> So, the difference is that when LINQ gets a text it can parse to extract
> the where part, it works, and if it finds a compiled function it gets the
> entire collection and brings every row to the function to check.
>
> Hanselman write about it, although this is just the sense of it not the
> details:
>
> http://www.hanselman.com/blog/TheWeeklySourceCode52YouKeepUsingThatLINQIDunnaThinkItMeansWhatYouThinkItMeans.aspx
>
> Now, one more catch is how to use it. Unfortunately you cannot use it with
> the query syntax (the "from ... in ... where .. select .."). You have to use
> the LINQ methods.
>
> Changing your example to use Expression::
>
> private void Test( Expression<Func<Person, bool>> predicate )
> {
> var query = Linq<Person>("person").Where( predicate );
>
>
> var resultList = query.ToList();
>
> Assert.That(resultList,
> Has.All.AssignableTo(typeof(Person)));
> }
>
>
> Side Note:
> The NHIbernare LINQ you are using (Recognized by seeing
> Session.Linq<...>()) is pretty old and no longer maintained. I advise you to
> the the LINQ provider in NHibernate itself. This is available in NHibernate
> 3.0 (which is pretty much backwards compatible with NHibernate 2.1.2 GA).
> You can either download the latest alpha or just the latest source code from
> SVN "trunk" folder. (yes, both are usually high quality, due to thousands of
> unit tests in there and also so many people using them in production, I'm
> one). Then you'll replace Session.Linq<>() with Session.Query().
> Note that all mentioned about expression trees and LINQ pretty much applies
> to any LINQ provider, not just those of NHibernate.
>
>
> Hope this helps.
>
> Regards,
>
>
>
> *Mohamed Meligy
> *Readify | Senior Developer
>
> M:*+61 451 835006* | W: www.readify.net
>
> [image: Description: Description: Description: Description:
> rss_16]<http://gurustop.net/>
> [image: Description: Description: Description: Description:
> cid:[email protected]] <http://www.linkedin.com/in/meligy>
> [image:
> Description: Description: Description: Description:
> cid:[email protected]] <http://twitter.com/meligy>
>
>
>
> On Wed, Sep 22, 2010 at 9:32 PM, manish.in.microsoft <
> [email protected]> wrote:
>
>> Thanks Oscar.
>>
>> I understood that NHibernate could not figure out that the predicate
>> was a lamdbda expression. If I change Func<Person, bool> to
>> Expression<Func<Person, bool>>, how will the Linq query change? I
>> believe I will no longer be able to use from ... where predicate(e)
>> select e?
>>
>> On Sep 22, 4:17 pm, Oskar Berggren <[email protected]> wrote:
>> > 2010/9/22 manish.in.microsoft <[email protected]>:
>> >
>> >
>> >
>> > > I have a severe performance problem with Linq for NHibernate that I am
>> > > able to reproduce with the Linq for NHibernate unit test cases as
>> > > well. Consider the following test case:
>> >
>> > > [TestFixture]
>> > > public class EntityNameTests : BaseTest
>> > > {
>> > > [Test]
>> > > public void CanQueryOnEntityName()
>> > > {
>> > > var query = (from e in session.Linq<Person>("person")
>> > > where e.Id == 1
>> > > select e);
>> >
>> > > var resultList = query.ToList();
>> >
>> > > Assert.That(resultList,
>> > > Has.All.AssignableTo(typeof(Person)));
>> > > }
>> > > }
>> >
>> > > When I run this test case, I see the following database query being
>> > > fired:
>> >
>> > > SELECT this_.Id as Id7_0_, this_.Name as Name7_0_ FROM Person this_
>> > > WHERE this_.Id = @p0;@p0 = 1
>> >
>> > > This is expected. However, if I change the test case to:
>> >
>> > > [TestFixture]
>> > > public class EntityNameTests : BaseTest
>> > > {
>> > > [Test]
>> > > public void CanQueryOnEntityName()
>> > > {
>> > > this.RunTest(e => e.Id == 1);
>> > > }
>> >
>> > > private void Test(Func<Person, bool> predicate)
>> > > {
>> > > var query = (from e in session.Linq<Person>("person")
>> > > where predicate(e)
>> > > select e);
>> >
>> > In this case, you are saying:
>> >
>> > ... where SomeRandomFunctionCallThatMightDoWhateverItLikes(e) ...
>> >
>> > NHibernate has no choice but to get everything and pass each item to
>> > the function. You need to use Expression<Func<T, bool>> instead.
>> >
>> > /Oskar
>>
>> --
>> You received this message because you are subscribed to the Google Groups
>> "nhusers" group.
>> To post to this group, send email to [email protected].
>> To unsubscribe from this group, send email to
>> [email protected]<nhusers%[email protected]>
>> .
>> For more options, visit this group at
>> http://groups.google.com/group/nhusers?hl=en.
>>
>>
>
--
You received this message because you are subscribed to the Google Groups
"nhusers" group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/nhusers?hl=en.
