org.apache.solr.search

Class SwitchQParserPlugin

  • All Implemented Interfaces:
    SolrInfoMBean, NamedListInitializedPlugin


    public class SwitchQParserPlugin
    extends QParserPlugin

    A QParserPlugin that acts like a "switch/case" statement.

    QParser's produced by this plugin will take their primary input string, trimmed and prefixed with "case.", to use as a key to lookup a "switch case" in the parser's local params. If a matching local param is found the resulting param value will then be parsed as a subquery, and returned as the parse result.

    The "case" local param can be optionally be specified as a switch case to match missing (or blank) input strings. The "default" local param can optionally be specified as a default case to use if the input string does not match any other switch case local params. If default is not specified, then any input which does not match a switch case local param will result in a syntax error.

    In the examples below, the result of each query would be XXX....

      q={!switch case.foo=XXX case.bar=zzz case.yak=qqq}foo
      q={!switch case.foo=qqq case.bar=XXX case.yak=zzz} bar  // extra whitespace
      q={!switch case.foo=qqq case.bar=zzz default=XXX}asdf   // fallback on default
      q={!switch case=XXX case.bar=zzz case.yak=qqq}          // blank input
     

    A practical usage of this QParsePlugin, is in specifying "appends" fq params in the configuration of a SearchHandler, to provide a fixed set of filter options for clients using custom parameter names. Using the example configuration below, clients can optionally specify the custom parameters in_stock and shipping to override the default filtering behavior, but are limited to the specific set of legal values (shipping=any|free, in_stock=yes|no|all).

     <requestHandler name="/select" class="solr.SearchHandler">
       <lst name="defaults">
         <str name="in_stock">yes</str>
         <str name="shipping">any</str>
       </lst>
       <lst name="appends">
         <str name="fq">{!switch case.all='*:*'
                                 case.yes='inStock:true'
                                 case.no='inStock:false'
                                 v=$in_stock}</str>
         <str name="fq">{!switch case.any='*:*'
                                 case.free='shipping_cost:0.0'
                                 v=$shipping}</str>
       </lst>
     </requestHandler>

    A slightly more interesting variant of the shipping example above, would be to combine the switch parser with the frange parser, to allow the client to specify an arbitrary "max shipping" amount that will be used to build a filter if and only if a value is specified. Example:

     <requestHandler name="/select" class="solr.SearchHandler">
       <lst name="invariants">
         <str name="shipping_fq">{!frange u=$shipping}shipping_cost</str>
       </lst>
       <lst name="defaults">
         <str name="shipping">any</str>
       </lst>
       <lst name="appends">
         <str name="fq">{!switch case='*:*'
                                 case.any='*:*'
                                 default=$shipping_fq
                                 v=$shipping}</str>
       </lst>
     </requestHandler>

    With the above configuration a client that specifies shipping=any, or does not specify a shipping param at all, will not have the results filtered. But if a client specifies a numeric value (ie: shipping=10, shipping=5, etc..) then the results will be limited to documents whose shipping_cost field has a value less then that number.

    A similar use case would be to combine the switch parser with the bbox parser to support an optional geographic filter that is applied if and only if the client specifies a location param containing a lat,lon pair to be used as the center of the bounding box:

     <requestHandler name="/select" class="solr.SearchHandler">
       <lst name="invariants">
         <str name="bbox_fq">{!bbox pt=$location sfield=geo d=$dist}</str>
       </lst>
       <lst name="defaults">
         <str name="dist">100</str>
       </lst>
       <lst name="appends">
         <str name="fq">{!switch case='*:*' 
                                 default=$bbox_fq 
                                 v=$location}</str>
       </lst>
     </requestHandler>