Hi, as you suggest, at the moment my strategy is to sort the result
afterwards and then to filter the required page.
However, if I have some time I would like to implement sorting in the JDBC
optimized visitor. In this way I would need to discriminate depending on
the data source, but performance will be much better on JDBC databases.
Regards,
César
2014-04-22 9:37 GMT+02:00 Jody Garnett <jody.garn...@gmail.com>:
> Looking at the internals of UniqueVisitor is uses:
>
> Set set = new HashSet();
>
> Can you sort this result yourself after calling the visitor? Or would you
> like to submit a patch to use TreeSet?
>
> Jody Garnett
>
>
> On Thu, Apr 17, 2014 at 7:42 PM, César Martínez Izquierdo <
> cesar....@gmail.com> wrote:
>
>> Hello,
>>
>> I am trying to run a distinct values query, which should be at the same
>> time sorted and paged (offset and limit). I have tried the following code
>> (simplified):
>>
>> Query query = new Query(typeName, Filter.INCLUDE, new String[]
>> {fieldName});
>> query.setSortBy(new SortBy[]{sortBy});
>> query.setStartIndex(startIndex);
>> query.setMaxFeatures(maxFeatures);
>> SimpleFeatureCollection featCol = featureSource.getFeatures(query);
>> Expression expr = factory.property(fieldName);
>> UniqueVisitor visitor = new UniqueVisitor(expr);
>> featCol.accepts(visitor, null);
>>
>> I have have correctly understood the documentation, the feature
>> collection is not changed by the visitor, but I can get the result by using:
>> List uniqueValues = visitor.getResult().toList();
>> However, this result is not ordered, thus making impossible to run
>> queries such as:
>> SELECT DISTINCT(name) FROM osmadmlv2
>> ORDER BY name asc OFFSET 50 LIMIT 10
>>
>> I found a previous conversation [1] suggesting to implement DISTINCT it
>> as a Hint, but that case could be solved by using the visitor (but I guess
>> they did not need sorting and paging).
>>
>> Is not possible to do such query, am I doing something wrong or is it a
>> bug in the implementation?
>>
>> Thanks in advance,
>>
>> César
>>
>> [1]
>> http://osgeo-org.1560.x6.nabble.com/distinct-query-hint-td5049204.html
>>
>> --
>> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>> César Martínez Izquierdo
>> GIS developer
>> - - - - - - - - - - - - - - - - - - - -
>> Blog: http://geotechnotes.wordpress.com/
>> ETC-SIA: http://sia.eionet.europa.eu/
>> Universitat Autònoma de Barcelona (SPAIN)
>> - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
>>
>>
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>
--
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César Martínez Izquierdo
GIS developer
- - - - - - - - - - - - - - - - - - - -
Blog: http://geotechnotes.wordpress.com/
ETC-SIA: http://sia.eionet.europa.eu/
Universitat Autònoma de Barcelona (SPAIN)
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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