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1. Re: OneToMany sorting
EJB3 provides a nice and elegant solution via the @OroderBy Annotation.
@Entity public class Course { ... @ManyToMany @OrderBy("lastname ASC") public List<Student> getStudents() {...}; ... } @Entity public class Student { ... @ManyToMany(mappedBy="students") @OrderBy // PK is assumed public List<Course> getCourses() {...}; ... }
Have a look at the EJB3 Persistence Specification (ejb-3_0-pfd-spec-persistence.pdf) on page 184 / Section 9.1.26 OrderBy Annotation.
Hope that helps
Alex
ejb3workshops.com
http://ejb3workshop.com -
2. Re: OneToMany sorting
Thank you Alex. However, I was aware of that particual annotation already. I probably didn't state my issue clearly. So I'll try again. When using the @OrderBy annotation I have no means of specifying (at runtime), by which column to sort the children, or do I?!
Second, lazy loading fills the children collection with all members, the very first time I use the getChildren() function. So, if I had e.g. 20000 children, all children would be read in at once, even if I only wanted to display the first 10 results.
So. I'm looking for something like:
@OneToMany(targetEntity=com.test.AbstractChild.class, cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy="parent")
@OrderBy(sortBy + " " + direction)
public Iterator getChildren(String sortBy, String direction);
or anything similar that gets the job done. Is any of my wishes fullfillable with EJB3 or hibernate's extensions of the spec? -
3. Re: OneToMany sorting
It look to me like a perfect example for a custom query. The EJB query language has support for sorting as well as paging, loading a limited subset like top 10 etc. via
The Query Interface/** * Set the maximum number of results to retrieve. * @param maxResult * @return the same query instance * @throws IllegalArgumentException if argument is negative */ public Query setMaxResults(int maxResult); /** * Set the position of the first result to retrieve. * @param start position of the first result, numbered from 0 * @return the same query instance * @throws IllegalArgumentException if argument is negative */ public Query setFirstResult(int startPosition);
Extracted from Enterprise JavaBeans 3.0, Proposed Final Draft - 3.5.1 Query Interface
Hope this is what you looking for. If you like an example please let me know I will have to dig one up that is to the point then.
Alex
ejb3workshop.com -
4. Re: OneToMany sorting
Alex! Thank's a lot. It goes into the right direction!
Do you think it would be possible to create such a custom Query and let it implement the Annotation interface and include the implementation of OneToMany, so that it could be used just like the OneToMany annotation (Cascades, etc.)?!
If you have a working example (no matter what), it would be great if you can provide it.
Thank's a lot.
Regards
d.j. -
5. Re: OneToMany sorting
Example :
Step 1: Create the QueryQuery query = manager.createQuery("select o ... ORDER BY o.id desc")
Step 2: Set Maximum Record Setquery.setMaxResults
Step 3: Set the index of the first recordquery.setFirstResult(10)
Step 4: Run the QueryList<Stuff> stuff = query.getResultList()
I hope this helps
Alex
ejb3workshop.com[/url] -
6. Re: OneToMany sorting
Guys, that's the second time I told you so, go to the USER forum.
http://www.jboss.com/index.html?module=bb&op=viewforum&f=221 -
7. Re: OneToMany sorting
i understand perfectly well that these question belong on the user forum. but i have arrived here a couple of times already posting without knowing that this is the design forum ..
i follow the trail : http://www.jboss.org -> Hot JBoss Products - JBoss EJB3 -> Forums (in the menu on the left)
shouldn't that lead me to the user forum instead of the design forum ?
just my 2ct .. -
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