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From Andrus Adamchik <>
Subject Re: [jira] [Updated] (CAY-1294) Generify query
Date Mon, 10 Dec 2012 10:09:27 GMT
A great approach to break our deadlock of on this feature! But maybe we leave a bit more room
for future extension by defining an interface for generics selecting query:

interface Select<T>

SelectQuery<T> extends QualifiedQuery implements Select<T>

List<T> performQuery(Select <T> query)

Then we can reuse the same ObjectContext method for other queries we might invent.


On Dec 10, 2012, at 9:05 AM, John Huss (JIRA) <> wrote:
>     [
> John Huss updated CAY-1294:
> ---------------------------
>    Attachment: 0002-Minimize-compiler-warnings-about-missing-type-parame.patch
>                0001-Add-type-parameter-to-SelectQuery-to-indicate-query-.patch
> Here is an implementation of a generified SelectQuery.  It doesn't require any new API
- there is simply an overloaded version of ObjectContext.performQuery for SelectQuery<T>
that returns List<T>.  
> <T> List<T> performQuery(SelectQuery<T> query);
> The <T> is unbounded because it has to support DataRows in addition to Persistent
objects.  The end result of course is that you can avoid having to cast the query result from
List to List<Artist> and you avoid the compiler warning.  This seems like a simple win
- any objections?
> I also added a static method to create an instance because if you use this you can avoid
repeating the class name twice, as in new SelectQuery<Artist>(Artist.class, null), which
feels very tedious.  So if you prefer you can call SelectQuery.from(Artist.class, null) instead
and it will infer List<Artist> as the query result type.
> public static <T> SelectQuery<T> from(Class<T> rootClass, Expression
>> Generify query
>> --------------
>>                Key: CAY-1294
>>                URL:
>>            Project: Cayenne
>>         Issue Type: Improvement
>>         Components: Core Library
>>           Reporter: Ari Maniatis
>>           Assignee: Andrus Adamchik
>>            Fix For: Undefined future
>>        Attachments: 0001-Add-type-parameter-to-SelectQuery-to-indicate-query-.patch,
>> Although most of the generics work has been completed for 3.0, 'query' is still largely
untouched. From a mailing list post by Andrus, here are possible query result types:
>> ? extends Persistent
>> ? extends Object (unfinished POJO implementation)
>> CayenneDataObject (as in "generic persistence" [1])
>> DataRow
>> scalar
>> Object[] (a mix of scalars and any of the above)
>> Certainly having a typed result list would be very useful in the most common case
of <? extends Persistent>.
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