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From "Tom Winch (JIRA)" <>
Subject [jira] [Updated] (SOLR-7341) xjoin - join data from external sources
Date Tue, 09 Feb 2016 12:52:19 GMT


Tom Winch updated SOLR-7341:
    Affects Version/s:     (was: 4.10.3)
        Fix Version/s: 4.10.3

> xjoin - join data from external sources
> ---------------------------------------
>                 Key: SOLR-7341
>                 URL:
>             Project: Solr
>          Issue Type: New Feature
>          Components: search
>            Reporter: Tom Winch
>            Priority: Minor
>             Fix For: 4.10.3, 5.3.1, Trunk
>         Attachments: SOLR-7341.patch-4_10, SOLR-7341.patch-5_3, SOLR-7341.patch-trunk
> h2. XJoin
> The "xjoin" SOLR contrib allows external results to be joined with SOLR results in a
query and the SOLR result set to be filtered by the results of an external query. Values from
the external results are made available in the SOLR results and may also be used to boost
the scores of corresponding documents during the search. The contrib consists of the Java
classes XJoinSearchComponent, XJoinValueSourceParser and XJoinQParserPlugin (and associated
classes), which must be configured in solrconfig.xml, and the interfaces XJoinResultsFactory
and XJoinResults, which are implemented by the user to provide the link between SOLR and the
external results source. External results and SOLR documents are matched via a single configurable
attribute (the "join field"). The contrib JAR solr-xjoin-4.10.3.jar contains these classes
and interfaces and should be included in SOLR's class path from solrconfig.xml, as should
a JAR containing the user implementations of the previously mentioned interfaces. For example:
> {code:xml}
> <config>
>   ..
>   <!-- XJoin contrib JAR file -->
>   <lib dir="${solr.install.dir:../../..}/dist/" regex="solr-xjoin-\d.*\.jar" />
>   ..
>   <!-- user implementations of XJoin interfaces -->
>   <lib path="/path/to/xjoin_test.jar" />
>   ..
> </config>
> {code}
> h2. Java classes and interfaces
> h3. XJoinResultsFactory
> The user implementation of this interface is responsible for connecting to an external
source to perform a query (or otherwise collect results). Parameters with prefix "<component
name>.external." are passed from the SOLR query URL to pararameterise the search. The interface
has the following methods:
> * void init(NamedList args) - this is called during SOLR initialisation, and passed parameters
from the search component configuration (see below)
> * XJoinResults getResults(SolrParams params) - this is called during a SOLR search to
generate external results, and is passed parameters from the SOLR query URL (as above)
> For example, the implementation might perform queries of an external source based on
the 'q' SOLR query URL parameter (in full, <component name>.external.q).
> h3. XJoinResults
> A user implementation of this interface is returned by the getResults() method of the
XJoinResultsFactory implementation. It has methods:
> * Object getResult(String joinId) - this should return a particular result given the
value of the join attribute
> * Iterable<String> getJoinIds() - this should return an ordered (ascending) list
of the join attribute values for all results of the external search
> h3. XJoinSearchComponent
> This is the central Java class of the contrib. It is a SOLR search component, configured
in solrconfig.xml and included in one or more SOLR request handlers. There is one XJoin search
component per external source, and each has two main responsibilities:
> * Before the SOLR search, it connects to the external source and retrieves results, storing
them in the SOLR request context
> * After the SOLR search, it matches SOLR document in the results set and external results
via the join field, adding attributes from the external results to documents in the SOLR results
> It takes the following initialisation parameters:
> * factoryClass - this specifies the user-supplied class implementing XJoinResultsFactory,
used to generate external results
> * joinField - this specifies the attribute on which to join between SOLR documents and
external results
> * external - this parameter set is passed to configure the XJoinResultsFactory implementation
> For example, in solrconfig.xml:
> {code:xml}
> <searchComponent name="xjoin_test" class="">
>   <str name="factoryClass">test.TestXJoinResultsFactory</str>
>   <str name="joinField">id</str>
>   <lst name="external">
>     <str name="values">1,2,3</str>
>   </lst>
> </searchComponent>
> {code}
> Here, the search component instantiates a new TextXJoinResultsFactory during initialisation,
and passes it the "values" parameter (1, 2, 3) to configure it. To properly use the XJoinSearchComponent
in a request handler, it must be included at the start and end of the component list, and
may be configured with the following query parameters:
> * results - a comma-separated list of attributes from the XJoinResults implementation
(created by the factory at search time) to be included in the SOLR results
> * fl - a comma-separated list of attributes from results objects (contained in an XJoinResults
implementation) to be included in the SOLR results
> For example:
> {code:xml}
> <requestHandler name="/xjoin" class="solr.SearchHandler" startup="lazy">
>   <lst name="defaults">
>     ..
>     <bool name="xjoin_test">true</bool>
>     <str name="xjoin_test.listParameter">xx</str>
>     <str name="xjoin_test.results">test_count</str>
>     <str name="xjoin_test.fl">id,value</str>
>   </lst>
>   <arr name="first-components">
>     <str>xjoin_test</str>
>   </arr>
>   <arr name="last-components">
>     <str>xjoin_test</str>
>   </arr>
> </requestHandler>
> {code}
> Note that, to include the list of join ids returned by the external source in the SOLR
results (likely for debug purposes), the value 'join_ids' may be specified in the "results"
> h3. XJoinQParserPlugin
> This query parser plugin constructs a query from the results of the external searches,
and is based on the TermsQParserPlugin. It takes the following local parameters:
> * method - as the TermsQParserPlugin, this specifies how to build the Lucene query
based on the join ids contained in external results; one of termsFilter, booleanQuery,
automaton, or docValuesTermsFilter (defaults to termsFilter)
> * v (or as usual with query parsers, specified via the query) - a Boolean combination
of XJoin search component names. Supported operators are OR, AND, XOR, and AND NOT
> The query is a Boolean expression whose terms are XJoin search component names. The resulting
set of join ids (obtained from the respective XJoin search components) are formed into a Lucene
query. Note that the join field of all the referenced XJoin search components must be identical.
Of course, the expression can be a single XJoin search component name in the simplest situation.
For example:
> {code}
> q={!xjoin}xjoin_test
> q={!xjoin v=xjoin_test}
> fq={!xjoin method=automaton}xjoin_test1 AND NOT xjoin_test2
> {code}
> h3. XJoinValueSourceParser
> This class provides a SOLR function that may be used, for example, in a boost function
to weight the result score from external values. The function returns an attribute value from
the external result with matching join attribute. There are two ways of using the function.
Either the XJoin component name is specified in the configuration parameters and the external
result attribute is the argument of the function in the query, or vice versa, the attribute
is specified in the configuration parameters and the component name is the function argument.
> The parameters for configuration in solrconfig.xml are:
> * xJoinSearchComponent - the name of an XJoin search component containing external results
> * attribute - the attribute to use from external results
> * defaultValue - if the external result has no such attribute, then this value is returned
> Normally, only one of xJoinSearchComponent and attribute is configured, but it
is possible to specify both (but you must specify at least one).
> For example:
> {code:xml}
> <valueSourceParser name="test_fn" class="">
>   <str name="xJoinSearchComponent">xjoin_test</str>
>   <double name="defaultValue">1.0</double>
> </valueSourceParser>
> {code}
> with corresponding query string parameter (for example) bq=test_fn(value)
> Alternatively:
> {code:xml}
> <valueSourceParser name="test_fn" class="">
>   <str name="attribute">value</str>
>   <double name="defaultValue">1.0</double>
> </valueSourceParser>
> {code}
> with corresponding query string parameter (for example) bq=test_fn(join_test)
> h3. Mapping between attributes and Java methods
> Java method names are converted into attribute (field) names by stripping the initial
"get" or "is" and converting the remainder from CamelCase to lowercase-with-underscores, and
vice versa. For example, getScore() converts to "score" and getFooBar() converts to "foo_bar",
and vice versa.
> The field list parameter of XJoinSearchComponent (fl) can be given as *, in which case
all methods beginning 'get' or 'is' are converted into fields in the SOLR result for the document.
> h2. Putting it together - the SOLR query URL
> Here is an example SOLR query URL to perform an xjoin:
> {noformat}
> http://solrserver:8983/solr/collection1/xjoin?defType=edismax&q=*:*&xjoin_test.external.q=foobar&fl=id,score&fq={!xjoin}xjoin_test&bf=test_fn(value)
> {noformat}
> This might result in the following SOLR response:
> {code:xml}
> <?xml version="1.0" encoding="UTF-8"?>
> <response>
>   <lst name="responseHeader">
>     <int name="status">0</int>
>     <int name="QTime">346</int>
>     <lst name="params">
>       ..
>     </lst>
>   </lst>
>   <result name="response" numFound="2" start="0" maxScore="58.60105">
>     <doc>
>       <str name="id">document1</str>
>       <float name="score">58.60105</float>
>     </doc>
>     <doc>
>       <str name="id">document2</str>
>       <float name="score">14.260552</float>
>     </doc>
>   </result>
>   <lst name="xjoin_test">
>     <int name="test_count">145</int>
>     <arr name="external">
>       <lst>
>         <str name="joinId">document1</str>
>         <lst name="doc">
>           <double name="value">7.4</double>
>         </lst>
>       </lst>
>       <lst name="external">
>         <str name="joinId">document2</str>
>         <lst name="doc">
>           <double name="value">2.3</double>
>         </lst>
>       </lst>
>     </arr>
>   </lst>
> </response>
> {code}
> Notes:
> * The actual 'join' is specified by the fq parameter. See XJoinQParserPlugin above.
> * The function test_fn is used in the bf score-boost function. Since the argument is
value2, that attribute of the external results is used as the score boost.
> h2. Many-to-many joins
> XJoin supports many-to-many joins in the following two ways.
> h3. Joining against a multi-valued field
> The SOLR field used as the join field may be multi-valued. External join values will
match every SOLR document with at least one matching value in the join field. As usual, for
every SOLR document in the results set, matching external results are appended. In this case,
this includes matching external results with join id values for every value from the multi-valued
field. Therefore, there may be many more external results included than the number of SOLR
> h3. Many external results with the same join id
> The case of many external results having the same join id is supported by returning a
Java Iterable from the implementation of XJoinResults.getResult(joinIdStr). In this case,
one <lst name="doc"> is added to the corresponding <lst name="external"> per element
in the iterable. For the XJoinValueSourceParser, the maximum value is taken from the set of
possible values.
> h2. Joining results from multiple external sources
> There are (at least) 3 different ways XJoin can be used in conjunction with other SOLR
features to combine results from more than one external source.
> h3. Multiple filter queries
> Multiple filter queries are ANDed together by SOLR, so if this is the desired combination
for external result join ids, this is a simple approach. (Note the implications for filter
caching.) In this case, the external join fields do not have to be the same.
> For example (assuming two configured XJoin components, xjoin_test and xjoin_other):
> {noformat}
> http://solrserver:8983/solr/collection1/xjoin?q=*:*&xjoin_test.external.q=foobar&xjoin_other.external.q=barfoo&fq={!xjoin}xjoin_test&fq={!xjoin}xjoin_other
> {noformat}
> h3. Nested queries in the standard SOLR Query Parser
> The nested query syntax of the standard SOLR query parser (see
can be used for more complicated combinations, allowing for "should", "must" etc. Lucene queries
to be built from external join id sets. The external join fields do not have to be the same.
> For example (again, assuming two configured XJoin components, xjoin_test and xjoin_other):
> {noformat}
> http://solrserver:8983/solr/collection1/xjoin?q=*:*&xjoin_test.external.q=foobar&xjoin_other.external.q=barfoo&fq=_query_:"{!xjoin}xjoin_test"
> {noformat}
> h3. Boolean expressions with the XJoin Query Parser
> To combine external join id sets directly using a Boolean expression, one can use the
XJoinQParserPlugin as detailed above. This allows arbitrary Boolean expressions using the
operators AND, OR, XOR and AND NOT.
> For example (again, assuming two configured XJoin components, xjoin_test and xjoin_other):
> {noformat}
> http://solrserver:8983/solr/collection1/xjoin?q=*:*&xjoin_test.external.q=foobar&xjoin_other.external.q=barfoo&fq={!xjoin}xjoin_test
XOR xjoin_other
> {noformat}

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