Add a weight scoring function to the search (toptal#380)

lib/chewy/query.rb

@@ -395,6 +395,28 @@ def boost_factor(factor, options = {})
       chain { criteria.update_scores scoring }
     end
 
+    # Add a weight scoring function to the search. All scores are
+    # added to the search request and combinded according to
+    # <tt>boost_mode</tt> and <tt>score_mode</tt>
+    #
+    # This probably only makes sense if you specify a filter
+    # for the weight as well.
+    #
+    #   UsersIndex.weight(23, filter: { term: { foo: :bar} })
+    #       # => {body:
+    #              query: {
+    #                function_score: {
+    #                  query: { ...},
+    #                  functions: [{
+    #                    weight: 23,
+    #                    filter: { term: { foo: :bar } }
+    #                  }]
+    #                } } }
+    def weight(factor, options = {})
+      scoring = options.merge(weight: factor.to_i)
+      chain { criteria.update_scores scoring }
+    end
+
     # Adds a random score to the search request. All scores are
     # added to the search request and combinded according to
     # <tt>boost_mode</tt> and <tt>score_mode</tt>

lib/chewy/search.rb

@@ -7,7 +7,7 @@ module Search
     included do
       singleton_class.delegate :explain, :query_mode, :filter_mode, :post_filter_mode,
         :timeout, :limit, :offset, :highlight, :min_score, :rescore, :facets, :script_score,
-        :boost_factor, :random_score, :field_value_factor, :decay, :aggregations,
+        :boost_factor, :weight, :random_score, :field_value_factor, :decay, :aggregations,
         :suggest, :none, :strategy, :query, :filter, :post_filter, :boost_mode,
         :score_mode, :order, :reorder, :only, :types, :delete_all, :find, :total,
         :total_count, :total_entries, to: :all

spec/chewy/query_spec.rb

@@ -127,6 +127,14 @@
     specify { expect(subject.boost_factor('23', filter: { foo: :bar}).criteria.scores).to eq([{ boost_factor: 23, filter: { foo: :bar } }]) }
   end
 
+  describe '#weight' do
+    specify { expect(subject.weight('23')).to be_a described_class }
+    specify { expect(subject.weight('23')).not_to eq(subject) }
+    specify { expect(subject.weight('23').criteria.scores).to eq([ { weight: 23  } ]) }
+    specify { expect { subject.weight('23') }.not_to change { subject.criteria.scores } }
+    specify { expect(subject.weight('23', filter: { foo: :bar}).criteria.scores).to eq([{ weight: 23, filter: { foo: :bar } }]) }
+  end
+
   describe '#random_score' do
     specify { expect(subject.random_score('23')).to be_a described_class }
     specify { expect(subject.random_score('23')).not_to eq(subject) }