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Re: Using GROUP By or @OrderColumn in JPA

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On 11/26/2015 1:28 AM, Cecil Westerhof wrote:
> On Thursday 26 Nov 2015 02:02 CET, Arne Vajhøj wrote:
>> On 11/25/2015 3:07 AM, Cecil Westerhof wrote:
>>> We are working on our first project with JPA. We had some bumps in
>>> the road, but I find it a good tool.
>>>
>>> We have an entity request which has a one to many relationship with
>>> estimate which has a one to one relationship with decision. One of
>>> the fields of decision is date.
>>>
>>> We need request-estimate-decision's where the date field of
>>> decision is not null and has the highest value. (We are only
>>> interested in the latest decision pro request.)
>>>
>>> I was thinking about a GROUP BY, but someone else thought about
>>> @OrderColumn. But if I understand it correctly an @OrderColumn
>>> needs an Integer and an index. We cannot change the database
>>> definition. So I suppose that @OrderColumn is not an option and we
>>> need to use the GROUP BY?
>>
>> How did you do it before with SQL?
>
> This was never done with SQL. They made a JPQL query that was badly
> written. I managed to help rewrite it, so it is a bit clearer what is
> happening. But everything was done over instant message, which is not
> ideal. Today we will meet face to face and I hope to get a better
> understanding of what they want and have.

I would probably do one of these:

1) Let JPA retrieve all decisions but add a getLastDecision
    method to the Estimate class. If the number of decisions
    per estimate is small then the overhead should be
    insignificant.

2) Don't let JPA map between estimates and decisions. Instead
    make a getLastDecision method in Estimate class that
    does a separate JPQL query to get the data. If the number
    of estimate for which you need last decision is small
    then the overhead should be insignificant.

Yes - I am arguing for a very simple solution. Unless you
really have a performance problem that requires a complex
solution then I strongly believe in keeping it simple.

Arne

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Using GROUP By or @OrderColumn in JPA Cecil Westerhof <Cecil@decebal.nl> - 2015-11-25 09:07 +0100
  Re: Using GROUP By or @OrderColumn in JPA Arne Vajhøj <arne@vajhoej.dk> - 2015-11-25 20:02 -0500
    Re: Using GROUP By or @OrderColumn in JPA Cecil Westerhof <Cecil@decebal.nl> - 2015-11-26 07:28 +0100
      Re: Using GROUP By or @OrderColumn in JPA Jerry Stuckle <jstucklex@attglobal.net> - 2015-11-26 08:25 -0500
      Re: Using GROUP By or @OrderColumn in JPA Arne Vajhøj <arne@vajhoej.dk> - 2015-11-26 20:22 -0500
        Re: Using GROUP By or @OrderColumn in JPA Silvio <silvio@internet.com> - 2015-11-27 12:28 +0100
          Re: Using GROUP By or @OrderColumn in JPA Jerry Stuckle <jstucklex@attglobal.net> - 2015-11-27 09:22 -0500
            Re: Using GROUP By or @OrderColumn in JPA Silvio <silvio@internet.com> - 2015-11-27 17:42 +0100
              Re: Using GROUP By or @OrderColumn in JPA Silvio <silvio@internet.com> - 2015-11-27 17:43 +0100
                Re: Using GROUP By or @OrderColumn in JPA Martin Gregorie <martin@address-in-sig.invalid> - 2015-11-27 18:21 +0000
          Re: Using GROUP By or @OrderColumn in JPA Arne Vajhøj <arne@vajhoej.dk> - 2015-11-28 23:01 -0500
            Re: Using GROUP By or @OrderColumn in JPA Silvio <silvio@internet.com> - 2015-11-29 12:42 +0100
        Re: Using GROUP By or @OrderColumn in JPA Arne Vajhøj <arne@vajhoej.dk> - 2015-11-28 22:44 -0500
      Re: Using GROUP By or @OrderColumn in JPA Martin Gregorie <martin@address-in-sig.invalid> - 2015-11-27 11:07 +0000

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