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Re: [eclipselink-users] Many-To-Many Remove Problem
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There are two ways objects are cached in EclipseLink, in the local
EntityManager cache, and the shared session/EntityManagerFactory cache.
I'm not sure which you encountered but refresh() will also refresh from the
database, so can solve your issue.
If you were using an existing EntityManager in your first screen, then it
would already have the objects registered in the persistence context before
you performed the merge/commit in the second EntityManager. Until you clear
or get a new EntityManager in the first screen it will continue to return
the same objects. An EntityManager is sometimes best used and one per
request/transaction.
There is also a shared cache by default in EclipseLink. This could result
in stale cached data if you had two different applications/server accessing
the same database. In this case you can refresh, use invalidation, or
disable the shared cache using "eclipselink.cache.shared.default"="false".
sonavor wrote:
>
> I think I have the problem solved.
>
> Although I have another case where I am calling an EntityManager merge on
> a JPA entity with a collection of objects that are of a many-to-many
> relationship .... and I haven't experience this problem, I was able to
> solve my problem in this case by using the EntityManager refresh method as
> follows:
>
> After I call the EntityManager merge on the updated MediaCategory entity,
> in the select method for the MediaCategory I do this now -
>
> MediaCategory mc = em.find(MediaCategory.class, catId);
> em.refresh(mc);
>
> That works.
>
> -sonavor
>
>
> sonavor wrote:
>>
>> I have a problem with updating a JPA entity where a many-to-many
>> relationship is involved. It appears to be some sort of session caching
>> issue but I can't find the source of the problem
>>
>> I can add items to my main entity and see that the many-to-many mapping
>> table updates with the results. When I re-select the main entity and
>> display the values it shows all of the mapped items. When I remove a
>> mapped item and re-select the entity the removed item(s) still show up in
>> the select query. However, if I look at the mapping table in the
>> database the items did remove correctly.
>>
>> My case is this -
>>
>> main table:
>> MEDIA_CATEGORY
>> category_id integer PK
>> cat_description varchar(50)
>>
>> second table:
>> KEYWORDS
>> kw_id integer PK
>> kw_name varchar(50)
>>
>> mapping table:
>> CATKWMAP
>> kw_id integer PK
>> category_id integer PK
>>
>> The MEDIA_CATEGORY JPA entity class is MediaCategory. Here are the
>> column to attribute mappings -
>>
>> @Column(name = "CATEGORY_ID", nullable = false)
>> private Integer categoryId;
>>
>> @Column(name = "CAT_DESCRIPTION")
>> private String catDescription;
>>
>> @JoinTable(name = "CATKWMAP", joinColumns = {@JoinColumn(name =
>> "CATEGORY_ID", referencedColumnName = "CATEGORY_ID")}, inverseJoinColumns
>> = {@JoinColumn(name = "KW_ID", referencedColumnName = "KW_ID")})
>> @ManyToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL)
>> private Collection<Keywords> catKwCollection;
>>
>> In my update code I just populate a MediaCategory class with the
>> categoryId, catDescription and a collection of keywords ( catKwCollection
>> );
>>
>> I then tell the EntityManager to merge the changes -
>>
>> em.merge(mediaCategory);
>>
>> After that occurs I checked the CATKWMAP table in the database and can
>> see that the submitted keyword-to-media_category mappings are there.
>> Whether the merge occurs where keywords are added or removed the database
>> table ends up with the correct results.
>>
>> If I add code to check the MEDIA_CATEGORY record right after the merge -
>>
>> MediaCategory mcUpdated = em.merge(mc);
>> Collection<Keywords> kwListing = mcUpdated .getCatKwCollection();
>> for (Iterator it = kwListing.iterator(); it.hasNext();) {
>> KwList kwl = (KwList) it.next();
>> log("updateMediaCategory - keyword: " + kwl.toString());
>> }
>>
>> The output shows keywords that match what the updated table has.
>>
>> But if I go to a screen where I select the updated MediaCategory ID and
>> have my code re-select the record using -
>>
>> MediaCategory mc = em.find(MediaCategory.class, categoryId);
>>
>> ...the mc.getCatKwCollection() contains all of the keywords I had prior
>> to the update. In other words, if my update removed some keyword
>> relationships and the table shows them removed, they still exist in this
>> selected MediaCategory instance.
>>
>> I have to stop my web application, restart it and re-select the
>> MediaCategory record in order to be in-sync with the database. What is
>> going on here? I tried adding a - em.flush() after my merge but it
>> didn't help.
>>
>> Thanks,
>> -sonavor
>>
>>
>>
>>
>>
>>
>>
>
>
-----
http://wiki.eclipse.org/User:James.sutherland.oracle.com James Sutherland
http://www.eclipse.org/eclipselink/
EclipseLink , http://www.oracle.com/technology/products/ias/toplink/
TopLink
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