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https://issues.apache.org/jira/browse/SLING-11230?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17513367#comment-17513367
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Dan Klco commented on SLING-11230:
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PR created:
https://github.com/apache/sling-org-apache-sling-jcr-resource/pull/21
> Extract Limit / Start From Query Comments in JCR Resource Provider
> ------------------------------------------------------------------
>
> Key: SLING-11230
> URL: https://issues.apache.org/jira/browse/SLING-11230
> Project: Sling
> Issue Type: Improvement
> Components: JCR
> Affects Versions: JCR Resource 3.2.0
> Reporter: Dan Klco
> Assignee: Dan Klco
> Priority: Minor
> Fix For: JCR Resource 3.2.2
>
>
> *Problem Statement*
> In addition to not supporting global limits, there are good reasons that a
> developer may want to return only a sub-set of the query results when
> executing a query. For example returning the 10 latest uploaded files.
> Currently this can be accomplished by executing a query and then only
> iterating to the 10th item, however a much larger query set may be fetched
> from the node store than required to service the intended use case.
> In addition, to support paging, the current implementation would require
> retrieving and iterating over the Resources until the desired start point is
> found then reading the subsequent Resources.
> _However_ changing the API contract for the ResourceResolver to either add a
> new method with the start and limit values would have a non-insignificant
> ripple effect into the implementations, mocks and providers which would be
> required to support this new method.
> *Recommended Solution*
> Instead, support parsing the start and limit values from the query via a
> comment at the end of the query in the form:
> /* slingQueryStart=9, slingQueryLimit=10 */
> This has the advantage of already being ignored by the Oak implementation of
> JCR-SQL2 and would be relatively easy to parse.
> The JCR Resource Provider's Query Language Provider could then remove the
> comment from the original query and set the limit and start values
> appropriately.
> *Alternative*
> Understandably, manipulating queries may not be desirable and there's a not
> insignificant possibility of backwards compatibility impact. As an
> alternative, I would recommend adding a new package to the API specifically
> for query support and in that provide a service interface and SPI for
> providers to implement which supports:
> - Queries with limits and offsets
> - Queries returning Streams as well as Iterators
> - Queries which automatically Adapt the result to the desired type
> - A SPI class for lazy adaptation of Stream and Iterators
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