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https://issues.apache.org/jira/browse/LUCENE-5207?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13865351#comment-13865351
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ASF subversion and git services commented on LUCENE-5207:
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Commit 1556508 from [~mikemccand] in branch 'dev/branches/lucene5376'
[ https://svn.apache.org/r1556508 ]
LUCENE-5207, LUCENE-5376: add expressions support to lucene server, so you can
define a virtual field from any JS expression and then sort by that field or
retrieve its values for all hits
> lucene expressions module
> -------------------------
>
> Key: LUCENE-5207
> URL: https://issues.apache.org/jira/browse/LUCENE-5207
> Project: Lucene - Core
> Issue Type: New Feature
> Reporter: Ryan Ernst
> Fix For: 4.6, 5.0
>
> Attachments: LUCENE-5207.patch, LUCENE-5207.patch, LUCENE-5207.patch
>
>
> Expressions are geared at defining an alternative ranking function (e.g.
> incorporating the text relevance score and other field values/ranking
> signals). So they are conceptually much more like ElasticSearch's scripting
> support (http://www.elasticsearch.org/guide/reference/modules/scripting/)
> than solr's function queries.
> Some additional notes:
> * In addition to referring to other fields, they can also refer to other
> expressions, so they can be used as "computed fields".
> * You can rank documents easily by multiple expressions (its a SortField at
> the end), e.g. Sort by year descending, then some function of score price and
> time ascending.
> * The provided javascript expression syntax is much more efficient than using
> a scripting engine, because it does not have dynamic typing (compiles to
> .class files that work on doubles). Performance is similar to writing a
> custom FieldComparator yourself, but much easier to do.
> * We have solr integration to contribute in the future, but this is just the
> standalone lucene part as a start. Since lucene has no schema, it includes an
> implementation of Bindings (SimpleBindings) that maps variable names to
> SortField's or other expressions.
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