On 3/17/2011 9:42 AM, Rainer Kwesi Schweigkoffer wrote:
> Hi Linda, all,
>
> Linda DeMichiel, am 11 Mar 2011 hast Du um 13:30 zum Thema "[jsr338-experts] outer joins with ON conditions" geschrieben :
>
>> For the criteria API equivalent, we could add methods
>>
>> on(Expression<Boolean> restriction);
>> and
>>
>> on(Predicate... restriction);
>>
>> to the Join interface.
>>
>> I'm not however sure what it is best that these methods return.
>
> What are your concerns against returning the Join instance they're
> residing on (i.e. overriding the method on the subinterfaces of Join
> declaring the respective type each) ?
>
I was wondering whether on() should return void. For example, in
the following, how do the Join objects relate?
// SELECT DISTINCT c
// FROM Customer c JOIN c.orders o
// ON c.address.city = o.shippingAddress.city
// JOIN o.product p
// ON o.quantity < p.inStock
CriteriaQuery<Customer> q = cb.createQuery(Customer.class);
Root<Customer> customer = q.from(Customer.class);
Join<Customer,Order> order = customer.join(Customer_.orders);
Join<Customer,Order> order2 =
order.on(cb.equal(customer.get(Customer_.address).get(Address_.city),
order.get(Order_.shippingAddress).get(Address_.city)));
Join<Order, Product> product = order.join(Order_.product); // or order2 ?
product.on(cb.lt(order.get(Order_.quantity), product.get(Product_.inStock)));
q.select(customer).distinct(true);
>> Finally, we should also discuss whether we should support the use of
>> ON with inner joins. SQL supports this, with the semantics that it is
>> equivalent to the use of WHERE.
>
> While I personally don't feel the desire to provide a second syntax of
> identical meaning, I fear, the way the criteria API has been designed
> practically forces us into this. And, as SQL does the same, it probably
> meets the expectations of the users...
>
Agreed. I think it is conceptually the simplest.
best regards,
-Linda
> Best regards
> Rainer
>
> ---
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