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https://issues.apache.org/jira/browse/LUCENE-7701?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alan Woodward updated LUCENE-7701:
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Attachment: LUCENE-7701.patch
Here's a patch implementing the idea. Group definitions are delegated to a
{{GroupSelector}} class, with the following methods:
* {{void setNextReader(LeafReaderContext ctx)}} - called per-segment
* {{State advanceTo(int doc)}} - advance the selector to a given doc. State
can be one of VALUE or SKIP
* {{T currentValue()}} - get the current group value
* {{T copyValue()}} - get a persistent copy of the current group value
* {{void setGroups(Collection<SearchGroup<T>> groups)}} - called to change the
selector to 'second-pass' mode. {{advanceTo(int)}} will return SKIP if the
currentValue is not in one of these groups.
There are two implementations of this, TermGroupSelector and
ValueSourceGroupSelector, replacing the current {{term}} and {{function}}
package Collectors.
The patch converts FirstPass, AllGroups, AllGroupHeads and
SecondPassCollectors. I haven't yet worked on the DistinctValues or GroupFacet
collectors, but they should be convertible in the same way.
> Refactor grouping collectors
> ----------------------------
>
> Key: LUCENE-7701
> URL: https://issues.apache.org/jira/browse/LUCENE-7701
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Alan Woodward
> Attachments: LUCENE-7701.patch
>
>
> Grouping currently works via abstract collectors, which need to be overridden
> for each way of defining a group - currently we have two, 'term' (based on
> SortedDocValues) and 'function' (based on ValueSources). These collectors
> all have a lot of repeated code, and means that if you want to implement your
> own group definitions, you need to override four or five different classes.
> This would be easier to deal with if instead the 'group selection' code was
> abstracted out into a single interface, and the various collectors were
> changed to concrete implementations.
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