[karmi#472] Added support for loading partial fields

See "Partial" in <http://www.elasticsearch.org/guide/reference/api/search/fields.html>

Closes karmi#472

lib/tire/search.rb

@@ -105,6 +105,11 @@ def fields(*fields)
         @fields = Array(fields.flatten)
         self
       end
+
+      def partial_field(name, options)
+        @partial_fields ||= {}
+        @partial_fields[name] = options
+      end
 
       def explain(value)
         @explain = value
@@ -156,6 +161,7 @@ def to_hash
           request.update( { :size => @size } )               if @size
           request.update( { :from => @from } )               if @from
           request.update( { :fields => @fields } )           if @fields
+          request.update( { :partial_fields => @partial_fields } ) if @partial_fields
           request.update( { :script_fields => @script_fields } ) if @script_fields
           request.update( { :version => @version } )         if @version
           request.update( { :explain => @explain } )         if @explain

test/unit/search_test.rb

@@ -414,6 +414,19 @@ def foo; 'bar'; end
         end
       end
 
+      context "with partial fields" do
+
+        should "add partial_fields config" do
+          s = Search::Search.new('index') do
+            partial_field 'name', :include => 'name_*'
+          end
+
+          hash = MultiJson.decode( s.to_json )
+          assert_equal({'name' => { 'include' => 'name_*'} }, hash['partial_fields'])
+        end
+
+      end
+
       context "explain" do
 
         should "default to false" do