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https://issues.apache.org/jira/browse/SOLR-1321?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12737596#action_12737596
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Andrzej Bialecki commented on SOLR-1321:
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If you follow the logic in getWildcardQuery, a field has to meet specific
requirements for this reversal to occur - namely, it needs to declare in its
indexing analysis chain that it uses ReversedWildcardFilter. This filter does
very special kind of reversal (prepending the marker) so it's unlikely that
anyone would use it for other purpose than to explicitly support leading
wildcards. So for now I'd say that users should consciously choose between this
method of supporting leading wildcards and the automaton wildcard query.
> Support for efficient leading wildcards search
> ----------------------------------------------
>
> Key: SOLR-1321
> URL: https://issues.apache.org/jira/browse/SOLR-1321
> Project: Solr
> Issue Type: Improvement
> Components: Analysis
> Affects Versions: 1.4
> Reporter: Andrzej Bialecki
> Fix For: 1.4
>
> Attachments: wildcards.patch
>
>
> This patch is an implementation of the "reversed tokens" strategy for
> efficient leading wildcards queries.
> ReversedWildcardsTokenFilter reverses tokens and returns both the original
> token (optional) and the reversed token (with positionIncrement == 0).
> Reversed tokens are prepended with a marker character to avoid collisions
> between legitimate tokens and the reversed tokens - e.g. "DNA" would become
> "and", thus colliding with the regular term "and", but with the marker
> character it becomes "\u0001and".
> This TokenFilter can be added to the analyzer chain that it used during
> indexing.
> SolrQueryParser has been modified to detect the presence of such fields in
> the current schema, and treat them in a special way. First, SolrQueryParser
> examines the schema and collects a map of fields where these reversed tokens
> are indexed. If there is at least one such field, it also sets
> QueryParser.setAllowLeadingWildcards(true). When building a wildcard query
> (in getWildcardQuery) the term text may be optionally reversed to put
> wildcards further along the term text. This happens when the field uses the
> reversing filter during indexing (as detected above), AND if the wildcard
> characters are either at 0-th or 1-st position in the term. Otherwise the
> term text is processed as before, i.e. turned into a regular wildcard query.
> Unit tests are provided to test the TokenFilter and the query parsing.
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