Hi Steve,
Please see the thread that started March 11, 2011. This should be available in the archives.
-Linda
On 5/24/2012 12:09 PM, Steve Ebersole wrote:
> I was not a member on the list when this was originally discussed, so I apologize for dragging up a potentially old
> discussion. But I wanted to caution against the use of 'ON' as a keyword in the way it is currently proposed in the
> specification.
>
> The problem is ambiguity in cases where the provider supports 'ON' as a more SQL-like ad-hoc joining capability between
> unassociated entities. In such cases the keyword 'ON' is often the only SYNTACTIC disambiguation between the 2 cases.
>
> Consider:
>
> select s.name, count(p.id)
> from javax.persistence.ex.Supplier s
> inner join javax.persistence.ex.Product p
> on s.id = p.supplierId
>
> So here we have Supplier and Product as unrelated classes (no mapped association). The problem is that structurally
> (syntactically) the query is completely ambiguous with the proposed form:
>
> select s.name, count(p.id)
> from javax.persistence.ex.Supplier s
> inner join s.product
> on p.status = 'inStock'
>
> where the join is an association join.
>
> When parsing queries its always better to disambiguate based on syntax whenever possible. Here we instead have to fall
> back to semantic disambiguation, which essentially means that we now have to hold parsing and interpret the meaning of
> the 2 sides of the join in oder to know what type of join it is.
>
> Not to mention that it is odd in my opinion for developers versed in SQL to see ON used here. The first thought is
> whether that adds to the SQL ON clause defined by the association mapping or whether that replaces it. So we lose a
> little intuitiveness.
>
> I'd really rather see a different keyword here. In Hibernate we chose WITH as the keyword for this for just these reasons:
>
> select s.name, count(p.id)
> from javax.persistence.ex.Supplier s
> inner join s.product
> with p.status = 'inStock'
>
> there I think it is very obvious that the condition is added to the SQL ON clause.
>