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Re: Using GROUP By or @OrderColumn in JPA

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On Thu, 26 Nov 2015 07:28:20 +0100, 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'd do it with an SQL query, but then I'm old fashioned. I'd join 
estimate and decision to form the result set ORDER it by date DESCENDING 
so the first entry in the result set is the latest decision. Adding an 
index on date to the database would speed up the sort, but if the result 
set is small the speed gain from adding an index should be minimal. 

From what others are saying, JPA should be able to achieve the same 
effect if its @OrderColumn annotation allows you to specify ascending or 
descending order.  



-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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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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