push a joins attribute to the facet

lib/forty_facets/filter/sql_facet_filter_definition.rb

@@ -6,6 +6,7 @@ def initialize(search, queries, opts)
       @search = search
       @queries = queries
       @path = Array(opts[:path]) if opts[:path].present?
+      @joins = Array(opts[:joins]) if opts[:joins].present?
       @path ||= @queries.keys
       @options = opts
     end
@@ -29,7 +30,7 @@ def build_scope
         Proc.new do |base|
           # intersection of values and definition queries
           base.where(selected_queries.values.map do |query|
-            "(#{query})" 
+            "(#{query})"
           end.join(" OR "))
         end
       end
@@ -55,13 +56,14 @@ def add(value)
 
       def facet
         query = definition.queries.map do |key, sql_query|
-          "(#{sql_query}) as #{key}" 
+          "(#{sql_query}) as #{key}"
         end.join(", ")
         query += ", count(*) as occurrences"
 
         counts = without.result.reorder("")
           .select(query)
           .group(definition.queries.keys)
+        counts = counts.joins(definition.joins) if definition.joins
         counts.includes_values = []
 
         result = {}

test/smoke_test.rb

@@ -23,6 +23,8 @@ class MovieSearch < FortyFacets::FacetSearch
   facet [:studio, :country], name: 'Country'
   facet [:studio, :status], name: 'Studio status'
   facet [:studio, :producers], name: 'Producers'
+  sql_facet({ uschis: "studios.name = 'Uschi'", non_uschis: "studios.name != 'USCHI'" },
+            { name: "Uschis", path: [:studio, :uschis], joins: [:studio] })
   sql_facet({ classic: "year <= 1980", non_classic: "year > 1980" },
             { name: "Classic", path: :classic })
   sql_facet({ classic: "year <= 1980", non_classic: "year > 1980" },
@@ -34,6 +36,12 @@ class MovieSearch < FortyFacets::FacetSearch
 
 class SmokeTest < Minitest::Test
 
+  def test_sql_facet_with_belongs_to
+    search = MovieSearch.new({'studio-uschis' => {}})
+    assert_equal Movie.count, search.result.size
+    assert_equal search.filter([:studio, :uschis]).facet, [FortyFacets::FacetValue.new(:uschis, 0, false), FortyFacets::FacetValue.new(:non_uschis, 40, false)]
+  end
+
   def test_it_finds_all_movies
     search = MovieSearch.new({})
     assert_equal Movie.all.size, search.result.size