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From Andrus Adamchik <and...@objectstyle.org>
Subject Re: Insert at a particular position in the detail list
Date Fri, 26 Sep 2008 19:52:05 GMT
That's a good point - we are trying to bridge the gap between OO and  
RDB worlds in a best possible way. And I wish we could do a reasonable  
ordering implementation (and without a join table). Otherwise the  
java.util.List "contract" is indeed broken.

Andrus


On Sep 26, 2008, at 10:39 PM, Robert Zeigler wrote:

> I disagree.  By the "intrinsic attribute" argument, we wouldn't be  
> trying to support inheritance and other useful features.
> The point of ORM is to bridge the gap that exists between Object  
> Models and Relational Models.  The fact is that, in java, at least,
> java.util.List is ordering-aware: you expect items that go into the  
> list to come back out in the same order.  So supporting the notion  
> of an ordered collection of items, particularly when the  
> relationship is mapped as a List,
> is probably "the right thing" to do.
>
> In fact, ordering /is/ an intrinsic database /operation/ on a  
> relationship, although not an intrinsic /attribute/.  But it happens  
> often enough that you /do/ care about the ordering of the  
> relationship that it would be awfully nice to /not/ have to override  
> the getter/setter to provide sorting.  This is, of course, how I've  
> done things in the past... and wished cayenne had built-in support  
> for ordered collections. Having the sorting occur in the getter is  
> inefficient; unless you take great pains to ensure that you don't re- 
> sort unless absolutely necessary, then every fetch of your list is  
> an o(n) operation, instead of just the first operation (which will  
> load the values, or at least the keys, from the db) being an O(n)  
> operation.  If we shifted the burden of managing ordered  
> relationships to cayenne, then cayenne can handle the complexity of  
> determining when a collection has been modified/needs to be  
> resorted, vs. when it doesn't, and we can minimize the effect of  
> having ordered collections.
>
> Finally, Hibernate and other ORM tools support this feature; I'm not  
> saying we should implement every feature of other ORMS; cayenne has  
> its set of strengths that appeal to the people who use it, and some  
> "features" of other ORMS are just a pain.  But I think this is one  
> case where supporting a feature supported by all of the major ORM  
> players would make Cayenne more competitive.
>
> So, from the "theoretical" perspective (what does an ORM do), from a  
> pragrmatic perspective (nice to offload and reuse the burden of  
> efficient sorted relationship management), and the "competition"  
> perspective, we really ought to support sorted lists.
>
> Robert
>
> On Sep 26, 2008, at 9/261:47 PM , Scott Anderson wrote:
>
>> Cayenne is there to abstract the interface to the tools that the
>> database provides, not to obfuscate the tools. Custom ordering is  
>> not an
>> intrinsic attribute of a relationship in the database; it should  
>> not be
>> an intrinsic attribute of a relationship in Java.
>>
>> If you need to sort the results or a JOIN, override the getter. If  
>> you
>> need to maintain custom ordering, model a linked list in your schema.
>> This just isn't Cayenne's responsibility.
>
>


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