package Elastic::Manual::QueryDSL;
$Elastic::Manual::QueryDSL::VERSION = '0.29_2'; # TRIAL
# ABSTRACT: How to use the Elasticsearch Query DSL

__END__

=pod

=encoding UTF-8

=head1 NAME

Elastic::Manual::QueryDSL - How to use the Elasticsearch Query DSL

=head1 VERSION

version 0.29_2

=head1 INTRODUCTION

Elasticsearch provides a rich query language, known as the
L<Query DSL|http://www.elasticsearch.org/guide/en/elasticsearch/reference/current/query-dsl.html> which
exposes much of the power of Lucene through a simple JSON interface.
It is tuned for full text search, but is in no way limited just
to that. It also provides very fast and flexible filters, ranges, geo-location
and more.

L<ElasticSearch::SearchBuilder> is a more concise, more Perlish version
of the Query DSL, similar to L<SQL::Abstract>.  Both syntaxes are
fully supported by Elastic::Model.
In L<Elastic::Model::View>, L<query|Elastic::Model::View/query>,
L<filter|Elastic::Model::View/filter> and
L<post_filter|Elastic::Model::View/post_filter> expect the native
Query DSL, while L<queryb|Elastic::Model::View/queryb>,
L<filterb|Elastic::Model::View/filterb> and
L<post_filterb|Elastic::Model::View/post_filterb> (note the extra "b") expect
the SearchBuilder syntax.

=head1 FULL TEXT VS EXACT MATCHING

There are two broad ways to match values in ElasticSearch:

=head2 Exact matching

=over

=item *

Documents where C<< status eq 'active' >>

=item *

Documents with any of the tags C<"perl">, C<"python"> or C<"ruby">

=item *

Documents published between 2012-01-01 and 2012-12-31

=item *

Documents within 50km of geo-point Lat,Lon

=item *

Documents that have a value in the C<name> field

=back

=head2 Full text matching

=over

=item *

Documents which are relevant to the search terms "quick brown fox"

=item *

Documents about "Big Mac", but not about "Apple Mac"

=item *

Documents about "flying kites", where the text may include "fly", "flying",
"kite" or "kites"

=item *

The most relevant auto-complete terms which match the partial phrase
"arnold schwa"

=back

You can only find what is actually stored in Elasticsearch.  For this reason,
exact matching is easy.  Full text matching is B<made> easy by the analysis
process, which you can read more about in L<Elastic::Manual::Analysis>.

=head1 QUERIES VS FILTERS

Every search has a single query, but that query can contain multiple other
queries and filters.   Choosing the right tool for the job is important:

=over

=item Filters:

=over

=item *

are for L</Exact matching> only

=item *

are boolean: a doc either matches or it doesn't. There is no scoring phase

=item *

are faster

=item *

are cacheable

=back

=item Queries:

=over

=item *

can be used for L</Exact matching> or for L</Full text matching>

=item *

score each document by "relevance" (see L<http://www.lucenetutorial.com/advanced-topics/scoring.html>
for a summary of how scoring works)

=item *

are slower, because of the scoring phase

=item *

are not cacheable

=back

=back

B<In summary>: you should use filters for any part of the query that does not
require relevance scoring.

B<Note:> a search for documents which have the exact tags C<"perl"> or C<"python">
may use a filter or a query.  If all you care about is that each document
has at least one of those tags, then use a filter.  If a document that has
BOTH tags should be considered more relevant than a document with only
one tag, then you need a query.

=head1 USING QUERIES AND FILTERS WITH ELASTIC::MODEL::VIEW

L<Elastic::Model::View> gives you a "view" across your data.  It is the
class you use to build your searches.

Just a query:

    $view->query(  text  => { title => 'object models'   })->search;

Just a filter:

    $view->filter( terms => { tags => ['perl','python' ] })->search

A query and filter combined:

    $view->query(  text  => { title => 'object models'   })
         ->filter( terms => { tags => ['perl','python' ] })->search

Or, with the SearchBuilder syntax:

    $view->queryb(  title => 'object models'    )
         ->filterb( tags  => ['perl','python' ] )->search

B<Note:> Elasticsearch only accepts a C<query> parameter, so the
L<query|Elastic::Model::View/query> and L<filter|Elastic::Model::View/filter>
attributes are combined at search time.  This means that you can quite happily
specify queries with nested filters using just the
L<query|Elastic::Model::View/query>  attribute.

B<Note:> the L<post_filter|Elastic::Model::View/post_filter> works in exactly
the same way as L<filter|Elastic::Model::View/filter>, but it only filters
the results AFTER the L<facets|Elastic::Model::View/facets> (like GROUP BY)
have been calculated.

=head1 QUERIES

See L<Elastic::Manual::QueryDSL::Queries> for examples of commonly used queries.

=head1 FILTERS

See L<Elastic::Manual::QueryDSL::Filters> for examples of commonly used filters.

=head1 AUTHOR

Clinton Gormley <drtech@cpan.org>

=head1 COPYRIGHT AND LICENSE

This software is copyright (c) 2014 by Clinton Gormley.

This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.

=cut
