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From Mike Kienenberger <mkien...@gmail.com>
Subject Re: Order By Expression
Date Tue, 16 Mar 2010 18:11:26 GMT
Michael,

I think you're misunderstanding him.

He's telling you exactly what he wants.

SELECT * FROM artist ORDER BY artist_name = 'Tom' DESC;

http://www.informit.com/articles/article.aspx?p=339935&seqNum=2

http://searchoracle.techtarget.com/answer/CASE-expressions-in-the-ORDER-BY-clause

I'm not sure if Cayenne supports it.  I've never seen that notation
before.  I don't think it supports expressions, only columns, in the
ordering.

I'd say it's a pretty database-specific function (but maybe I'm wrong).


On Tue, Mar 16, 2010 at 1:53 PM, Michael Gentry <mgentry@masslight.net> wrote:
> Hi Dave,
>
> You are close, but not quite there.  The ordering only applies to a
> column (artistName), but you are giving it a qualifier/expression
> (artistName = 'Tom').  You need to create the expression separately
> (multiple ways to do that, but I'll show one):
>
> Expression expression = ExpressionFactory.match("artistName", "Tom");
> SelectQuery query = new SelectQuery(Artist.class, expression);
> query.addOrdering("artistName", SortOrder.DESCENDING);
> context.performQuery(query);
>
> You might want to look at:
>
> http://cayenne.apache.org/doc30/parameterized-queries.html
> http://cayenne.apache.org/doc30/api/org/apache/cayenne/exp/ExpressionFactory.html
> http://cayenne.apache.org/doc30/api/org/apache/cayenne/exp/Expression.html
>
> Expressions are where you do the WHERE clause.  Also, instead of
> hardcode "artistName", you probably have Artist.ARTIST_NAME_PROPERTY
> available as a constant which is safer to use.
>
> mrg
>
>
> On Tue, Mar 16, 2010 at 1:33 PM, Dave Dombrosky <dombrd@gmail.com> wrote:
>> Yes I'm using Cayenne 3.  I'm not sure if I stated the problem in
>> enough detail, because it seems like you guys are confused.  Or maybe
>> I just don't understand how to use what you are telling me about.
>>
>> Maybe it would be better if I was helped with a full example.  Using
>> the Artist class from Cayenne's test schema, how would I go about
>> creating a SelectQuery to order all artists with the name "Tom" first?
>>  Basically to generate a query similar to this:
>>
>> SELECT * FROM artist ORDER BY artist_name = 'Tom' DESC;
>>
>> Would it be like this?
>>
>> SelectQuery query = new SelectQuery(Artist.class);
>> query.addOrdering("artistName = 'Tom'", SortOrder.DESCENDING);
>> context.performQuery(query);
>>
>> Because that still gets the error Unsupported ordering expression:
>> artistName = 'Tom'.
>>
>> Am I doing something wrong, or is this impossible with a SelectQuery?
>> I'd rather not use SQLTemplate if I can avoid it.
>>
>> -Dave
>>
>> On Tue, Mar 16, 2010 at 8:39 AM, Michael Gentry <mgentry@masslight.net> wrote:
>>> Hi Dave,
>>>
>>> Since you are seeing deprecation warnings I'm assuming you are using
>>> Cayenne 3?  If so, you should use:
>>>
>>> addOrdering(Ordering ordering) or
>>> addOrdering(String sortPathSpec, SortOrder order)
>>>
>>> These are defined for your SelectQuery object.  Of course, if you are
>>> using the first of those methods, you'll have to create your own
>>> Ordering object first.  The second creates one for you behind the
>>> scenes.
>>>
>>> Let me know if you need additional pointers!
>>>
>>> mrg
>>>
>>>
>>> On Tue, Mar 16, 2010 at 1:11 AM, Dave Dombrosky <dombrd@gmail.com> wrote:
>>>> Is there any way to use sort expressions in a query?  Something like
>>>> "ORDER BY column = id"?  I get the error "Unsupported ordering
>>>> expression" when trying to execute a query with this in it.
>>>>
>>>> Also, it looks like I might be able to do this using in-memory
>>>> sorting, but the Ordering(Expression sortExpression, ...) methods are
>>>> deprecated.  So what's the preferred way to sort on expressions in
>>>> Cayenne?
>>>>
>>>> -Dave
>>>>
>>>
>>
>

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