Yes,
We definitely would not want users changing the contents of
collections through read queries. This would open a lot of usability
issues with merging and change detection.
--Gordon
Linda DeMichiel wrote:
>
>
> On 3/17/2011 1:30 AM, Emmanuel Bernard wrote:
>> On 16 mars 2011, at 20:15, Linda DeMichiel wrote:
>>
>>>
>>> On 3/16/2011 3:46 AM, Emmanuel Bernard wrote:
>>>> On 15 mars 2011, at 19:16, Linda DeMichiel wrote:
>>>>> JPQL would be:
>>>>>
>>>>> FROM Cat as cat LEFT JOIN Kittens k ON k.bodyWeight > 10.0 AND
>>>>> k.parentName = cat.Name
>>>> But in this case, the SQL would be
>>>> from Cat c OUTER JOIN Kitten k ON c.id = k.parent AND c.name =
>>>> k.parentName AND k.bodyWeight > 10.0
>>>> which is one to many clause for what the user wants to do.
>>> No, the above would not add c.id = k.parent to the SQL ON clause.
>>>
>>> Since we only defined JOIN that involves relationship navigation, we
>>> can make this distinction.
>>>
>>
>> Got it now, sorry for having been dense :)
>>
>> For completion, one case we would not be able to support is to map
>> this full ON clause definition on an existing association at the
>> object level.
>>
>> Instead of:
>> String queryAssumingFullOnRewriting =
>> "select c from Cat c left join fetch c.kittens on c.name =
>> k.parentName AND k.bodyWeight > 10.0";
>> TypedQuery<Cat> cats = em.createQuery( queryAssumingFullOnRewriting
>> ).getResultList(); for (Cat cat : cats) {
>> Cat kittenJoinedByNameAndHealthy = cat.getKittens();
>> doStuff(kittenJoinedByNameAndHealthy);
>> }
>
> We don't currently support this however, since fetch joins are not
> permitted to specify
> an identification variable for objects referenced on the right side of
> the fetch
> join clause. You've cheated a bit above by sneaking in the "k." :-)
>
> We can still allow the use of ON with fetch joins, but it could
> reference the left
> hand side only.
>
>>
>> People would need to use tuples
>>
>> String adHocOn = "select c,k from Cat c left join Cat k on c.name
>> = k.parentName AND k.bodyWeight > 10.0";
>> TypedQuery<Tuple> cats = em.createQuery( adHocOn ).getResultList();
>> for (Tuple cat : cats) {
>> Cat cat = (Cat) tuple.get(0);
>> Cat kittenJoinedByNameAndHealthy = (Cat) tuple.get(1);
>> doStuff(kittenJoinedByNameAndHealthy);
>> }
>>
>> That's the only case I can think of when WITH vs ON could make sense.