Re: [eclipselink-users] Many-To-Many Remove Problem

[sonavor <jw@xxxxxxxxxxxxxx>]

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
> 
> 
> 
> 
> 
> 
> 

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