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matan_a
 Post subject: Help with HQL
PostPosted: Fri Aug 27, 2004 12:02 pm 
Newbie

Joined: Thu Jun 03, 2004 2:10 am
Posts: 19
Hibernate version: 2.1.6

I was wondering if anyone could help me out with HQL. I have three mapped objects:

Code:
<class name="Industry" table="industry" mutable="false">
       <id name="industryId"
            type="long"
            column="industry_id"
            unsaved-value="-1">
        <generator class="assigned"/>
        </id>
       
        .....

        <set name="categories" inverse="true" lazy="false">
            <key column="industry_id" />
            <one-to-many class="Cat" />
        </set>
</class>


Code:
<class name="Cat" table="cat" mutable="false">

        <id name="catId"
            type="long"
            column="cat_id"
            unsaved-value="-1">
            <generator class="assigned"/>
        </id>

        .....

        <many-to-one name="industry"
            class="Industry"
            column="industry_id">
            <meta attribute="use-in-tostring">true</meta>
        </many-to-one>

        <set name="projects" lazy="true" table="project_cat">
            <key column="cat_id" />
            <many-to-many class="Project" column="project_id" />
        </set>
</class>


Code:
<class name="Project" table="project">
         <id name="projectId"
            type="long"
            column="project_id"
            unsaved-value="-1">
            <generator class="native"/>
        </id>

        ....

        <property name="expirationDate"
            column="expiration_date"
            type="timestamp"
            not-null="false"
            index="idx_project_expiration_date">
        </property>

        <set name="categories" lazy="true" inverse="true" table="project_cat">
            <key column="project_id" />
            <many-to-many class="Cat" column="cat_id" />
        </set>
</class>




The relationship is that an industry has categories in it. Each project is listed under one or more of those categories - so that each project can technically be in more than one industry.

My goal is to return a list that shows each industry id (industryId) and the number of projects in that industry (count(industryId)). The main catch is that a project should not be counted twice if it's in more than one category in that industry.

In SQL, the statement is pretty straight-forward:

Code:
SELECT c.INDUSTRY_ID, COUNT(c.INDUSTRY_ID)
FROM
(SELECT DISTINCT c.INDUSTRY_ID, p.PROJECT_ID
FROM project_cat pc, cat c, project p
WHERE pc.cat_id = c.cat_id
AND p.PROJECT_ID = pc.project_id
AND p.EXPIRATION_DATE > current_date)
c GROUP BY c.INDUSTRY_ID


I have tried for a while now to get the same result using HQL and i haven't really gotten anywhere :(.

Any help would be appreciated!
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rhobot
 Post subject:
PostPosted: Fri Aug 27, 2004 3:50 pm 
Regular
Regular

Joined: Fri Aug 29, 2003 12:48 pm
Posts: 63
Do you even want category to be a real entity object? If there's nothing more to it than what you show, wouldn't it be simpler to do many-to-many mappings from Industry to Product?

Code:
<class name="Industry">
  ...
  <set name="products" table="cat">
    <key column="industry_id"/>
    <many-to-many class="Product" column="product_id"/>
  </set>
</class>


Then you could use count(elements(Industry.products)) in your hql query.

Note I'm by no means a Hibernate expert, just trying to help out.
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matan_a
 Post subject:
PostPosted: Fri Aug 27, 2004 4:53 pm 
Newbie

Joined: Thu Jun 03, 2004 2:10 am
Posts: 19
Categories are important in the system.

Do you know a way to solve the problem i stated in the message?

Thanks.
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rhobot
 Post subject:
PostPosted: Fri Aug 27, 2004 5:14 pm 
Regular
Regular

Joined: Fri Aug 29, 2003 12:48 pm
Posts: 63
The elements() function provided by HQL might have some help for you. Or you could just use the SQL query you already have written. I very much appreciate everything Hibernate does for me, but note that this piece of the puzzle - queries involving collections - can be more painful than not when all is said and done.
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matan_a
 Post subject:
PostPosted: Tue Aug 31, 2004 2:41 pm 
Newbie

Joined: Thu Jun 03, 2004 2:10 am
Posts: 19
Thanks for the reply.

I did solve the problem in the end, so I thought i'd post the solution for anyone else that might have a similar problem:

Code:
select
    cat.industry.id, count(distinct proj.id)
from
    Cat cat, Project proj join proj.categories pcat
where
    pcat.id = cat.id
    and proj.expirationDate > :expiration
group by
    cat.industry.id



Cheers.
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