Using nHibernate 1.01 in Visual Studio 2003 .net 1.1

I am using nHibernate in my application, but i just wanted to asked if there was a more effiect way of accessing the data than i have been doing.


Example of what im going:

I have four objects that are utilizing NHibernate Fair, Stand and Exhibitor and User

There are multiple Fairs and each Fair contains multiple Stands and each Stand contains one Exhibitor and each Exhibitor contains one user.

And what i want to do is given a User Id find all the Fairs they have a stand at.

So i have written this piece of code to do it:

IList l = fairdao.getFairs(); //calls a named query that get all fairs
IList attendedFairs = new ArrayList();

foreach(Fair f in l)
{
IList stands = f.Stands;

foreach(Stand s in stands)
{
Exhibitor ex = s.Exhibitor;

if(ex.User.Id==1)
{
attendedFairs.Add(f);
break;

}

}

}


While this does the job, it just appears to me the i could utilize hibernates functionality better. Could you give me afew pointers. Thanks

Iv tried this:

<query name="Fair.GetAttending">from Fair fair inner join fair.Stands stands where stands.Exhibitor.VcfUser.Id = ?</query>

But this returns a nasty list of fairs and stands.....how do i get this to only returns fairs?

hi bosh,

ah.. the Fair[] collection.. yeah that sounds familiar... this happens when
the query returns more than one type of object, sorry my fault... :/

add: 'select fair' to the query and your results will only contain the 'Fairs'.

How about the opposite of this?

Get all fairs
where for all stands the Exhibitor.User.Id is not qual to ?

I was going to try:

select fair from Fair fair inner join fair.Stands stands where stands.Exhibitor.User.Id != ?

But this will bring back any fair where any one of the users is not the id....i want all the users to not have the id

Hi guys.

Can you shed any light on this?

use the elements( ) keyword

Im struggling.....this dont seem to work..

select fair from Fair fair inner join fair.Stands stands where elements(stands.Exhibitor.VcfUser.Id) != 21


produces this error:

NHibernate.QueryException: dereferenced: Id [select fair from vcf.code.entites.Fair fair inner join fair.Stands stands where elements(stands.Exhibitor.VcfUser.Id) != 21]

Elements receives an association path ending with a collection (not a property as you used it with). AFAIK this situation of yours is solved in a more SQL like way:

from parent
where exists( select child.id from child where child.parentid = parent.id and
child.someprop.id != 21)

another way would be using ICriteria (doesn't really apply to you case but is realated).

criteria = CreateCriteria(Parent)
subc = criteria.CreateAlias("ChildList", "c"))
.Add( Expression.Eq( "c.x.y.z", 1 ) )

criteria.SetResultTransformer( CriteriaUtil.DistinctRootEntity ).List();

Dragos

dragos, could you elaborate on the 'setresulttransformer' ? I've never seen it mentioned in any documentation.

Thanks for the help....im probs being dumb, coz i dont fully see how this resolves my problem...

I tried this initially, and it returned nothing:





Was as this works:




What is the difference? usrly they work out as the same thing?

OK, so you want all fairs where a specific exhibitor did not participate:

The following should bring you all fairs for which no stand exists having the user x.

from Fair fair
where not exists( select stand from Stand stand where stand.Fair.Code = fair.id and stand.Exhibitor.VcfUser.id = 21)

The following will bring you fairs where there is at least another participant other than your exhibitor:

from Fair fair
where exists( select stand from Stand stand where stand.Fair.Code = fair.id and stand.Exhibitor.VcfUser.id != 21)

About setresulttransformer, it'a a method on ICriteria that transforms the result set. By design, ICriteria generated SQL so works with cartesian products. The result transformers get the query result as input and modify information according to some rule.

For example
select f from Fair inner f join f.stands
returns an IList with the same fair appearing multiple times. Using DistinctRootEntity you force NHibernate to remove duplicates fairs from the result retrieving something like distinct fairs.

Hope it helps

haha, thanks for that information. I had built my own helper functions for that!