[jpa-spec users] [jsr338-experts] Re: JPQL: Sorting on optional references

From: Oliver Gierke <>
Date: Wed, 29 Aug 2012 06:26:21 -0700

The problem is that adding an order by clause leaks a side effect into what is actually returned from the query, which shouldn't be the case.

Yes, it's outlined in the spec but it's also inconsistent in regards of mapping metadata being applied to the JPQL expression. An @Column(name = "Foo") get's regarded, why shouldn't an @ManyToOne(optional = true) be?

I think it get's more obvious if you consider a more simple case:

select p from Person p


select p from Person p order by

The former includes people without addresses, the latter does not? And this is totally inexplainable from a pure mapping metadata point of view. I wonder why the two lines defining path expressions being forced into inner joins have made it into the spec in the first place. Were the side effects not considered? Why explicitly not applying the mapping metadata?


PS: I've summarized my findings in this gist ( The comments might be interesting to consider.

Am 29.08.2012 um 14:47 schrieb Steve Ebersole <>:

> Not sure how this "side-effect" is "unpleasant and not easy to grasp".
> It is explicitly called out in the spec.
> -1 for changing implicit joins to result in inner or outer joins
> depending on the mapping. In such a case you can no longer see what
> will happen just by looking at the query itself, which in my opinion is
> far more "unpleasant and not easy to grasp".
> On 08/28/2012 07:44 AM, Oliver Gierke wrote:
>> Hi all,
>> I just came across a JPQL spec scenario that seems to be a bit weird and I wonder whether there's something we should do about. Suppose you have a Person with optional Addresses:
>> @Entity
>> class Person {
>> @OneToOne(nullable = true) Address address;
>> }
>> @Entity
>> class Address {
>> String city;
>> }
>> Now the query scenario here is that we'd like to get all Persons sorted by the Address' city:
>> select p from Person p left outer join p.address order by
>> Surprisingly, this query will not return Persons not having an Address associated for the following reason: JPA 2.0 spec section 4.4.4. defines path expressions as follows:
>>> Path expression navigability is composed using “inner join” semantics. That is,
>>> if the value of a non-terminal field in the path expression is null, the path is
>>> considered to have no value, and does not participate in the determination of
>>> the result.
>> That apparently forces persistence providers into adding an additional inner join to the query which rules out the Persons without Addresses in the first place. I think it's rather unfortunate to have this path expression definition applied to order by clauses as users probably don't expect adding a sort definition would strengthen the actual query criteria. So here are my questions:
>> 1. Why was the path expression navigability defined as such in the first place and not as considering the mapping metadata (nullable = true -> outer join, nullable = false -> inner join). Not saying this is utterly wrong, just want to understand the probably available reasons.
>> 2. Should/can this definition be changed to require consideration of the mapping information? The path expression definition is very much written with the purpose of defining selection criterias which is what they are effectively not used for when used in ORDER BY clauses. The current state leaves JPQL in the weird state that adding a sorting criteria affects the returned items not only in order but also in which items are returned at all, a side-effect which is unpleasant and not easy to grasp.
>> Cheers,
>> Ollie

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