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https://issues.apache.org/jira/browse/SOLR-2026?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12899253#action_12899253
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Lance Norskog commented on SOLR-2026:
-------------------------------------

Here's a use case: field collapsing. Some people currently do field collapsing 
with 2 queries: first you get a few hundred documents with just the id and 
_collapsar_ field. Then you trim the id set from the collapsar contents. and 
grab the first N unique ids. This is fine when you don't really care how many 
docs are in each collapsar group, you only care that there is more than one 
item per group.

This works great as a 2-query sequence where the code analyses the first return 
to create the second query.



> Need infrastructure support in Solr for requests that perform multiple 
> sequential queries
> -----------------------------------------------------------------------------------------
>
>                 Key: SOLR-2026
>                 URL: https://issues.apache.org/jira/browse/SOLR-2026
>             Project: Solr
>          Issue Type: New Feature
>          Components: SearchComponents - other
>            Reporter: Karl Wright
>            Assignee: Simon Willnauer
>            Priority: Minor
>             Fix For: 4.0
>
>         Attachments: SOLR-2026.patch, SOLR-2026.patch
>
>
> Several known cases exist where multiple index searches need to be performed 
> in order to arrive at the final result.  Typically, these have the constraint 
> that the results from one search query are required in order to form a 
> subsequent search query.  While it is possible to write a custom 
> QueryComponent or search handler to perform this task, an extension to the 
> SearchHandler base class would readily permit such query sequences to be 
> configured using solrconfig.xml.
> I will be therefore writing and attaching a patch tomorrow morning which 
> supports this extended functionality in a backwards-compatible manner.  The 
> tricky part, which is figuring out how to funnel the output of the previous 
> search result into the next query, can be readily achieved by use of the 
> SolrRequestObject.getContext() functionality.  The stipulation will therefore 
> be that the SolrRequestObject's lifetime will be that of the entire request, 
> which makes complete sense.  (The SolrResponseObject's lifetime will, on the 
> other hand, be limited to a single query, and the last response so formed 
> will be what gets actually returned by SearchHandler.)

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