Question

In my application I have Documents and Comments. A Comment belongs to exactly one Document, a Document can have several Comments.

I have a fairly complicated named query on my Documents:

<query name="public.documents">
    <![CDATA[
       from Document d join d.someOtherProperty join ...
       where 
           ...
]]>
</query>

The result set of this query should now be filtered according to several criteria. Unlike all the examples I could find on Hibernate Filters these properties are not in the Document class but in the Comment class. For example I would like to be able to add a filter which only shows me the Documents from the result set which have Comments by a particular author or which have Comments that were added on a certain date. Or both aforementioned restrictions.

Right now I do it like this:

<query name="public.documents.restricted.to">
    <![CDATA[
       from Document d join d.someOtherProperty join ...
       where 
           ...
           AND d.id IN (:restrictedTo)
]]>
</query>

This is a very ugly way to achieve my goal. Can I do this with a hibernate filter? I understood that filter is only a thin wrapper for additional where arguments, in my case I would need some sort of join.

If it can’t be done using a filter can you point me towards a different solution, I think this is a fairly common problem and I think that writing a query for each and every possible combination of restriction criteria is far from elegant.

Answer 1

I have not tried it, but I believe you can do this with filters.

As well as filtering entities, filters can be used to filter collections, such as the collection of Comments related to a Document.

You define filters for the Comments and activate these, something like this on the Doucment entity:

<set ...>
    <filter name="commentMadeAfter" condition=":commentDate <= commentDate"/>
    <filter name="commentMadeBy" condition=":commentUser = userId"/>
</set>

This will then restrict the comments retrieved on each document to the specified criteria. To ensure the returned documents only contain comments that match this criteria, you also add a filter (or a where clause to the query) to exclude documents with no comments from the result set.

There is an example of something similar on the spring forums.