Consistently use FacetField#field when retrieving aggregation values …

…from the response

app/controllers/concerns/blacklight/facet.rb

@@ -19,21 +19,28 @@ def facets_from_request(fields = facet_field_names)
     end
 
     def facet_field_names
-      blacklight_config.facet_fields.keys
+      blacklight_config.facet_fields.values.map(&:field)
     end
 
+    # @param [String] field Solr facet name
+    # @return [Blacklight::Configuration::FacetField] Blacklight facet configuration for the solr field
     def facet_configuration_for_field(field)
-      blacklight_config.facet_fields[field] ||
-        blacklight_config.facet_fields.values.find { |v| v.field.to_s == field.to_s } ||
+      # short-circuit on the common case, where the solr field name and the blacklight field name are the same.
+      return blacklight_config.facet_fields[field] if blacklight_config.facet_fields[field] && blacklight_config.facet_fields[field].field == field
+
+      # Find the facet field configuration for the solr field, or provide a default.
+      blacklight_config.facet_fields.find { |_, v| v.field.to_s == field.to_s } ||
         Blacklight::Configuration::FacetField.new(field: field).normalize!
     end
 
     # Get a FacetField object from the @response
     def facet_by_field_name(field_or_field_name)
       case field_or_field_name
-      when String, Symbol, Blacklight::Configuration::FacetField
+      when String, Symbol
         facet_field = facet_configuration_for_field(field_or_field_name)
-        @response.aggregations[facet_field.key]
+        @response.aggregations[facet_field.field]
+      when Blacklight::Configuration::FacetField
+        @response.aggregations[field_or_field_name.field]
       else
         # is this really a useful case?
         field_or_field_name

spec/helpers/facets_helper_spec.rb

@@ -104,13 +104,13 @@
 
   describe "facet_by_field_name" do
     it "retrieves the facet from the response given a string" do
-      facet_config = double(:query => nil, field: 'a', key: 'a')
+      facet_config = double(query: nil, field: 'b', key: 'a')
       facet_field = double()
-      allow(helper).to receive(:facet_configuration_for_field).with(anything()).and_return(facet_config)
+      allow(helper).to receive(:facet_configuration_for_field).with('b').and_return(facet_config)
       @response = double()
-      allow(@response).to receive(:aggregations).and_return('a' => facet_field)
+      allow(@response).to receive(:aggregations).and_return('b' => facet_field)
 
-      expect(helper.facet_by_field_name('a')).to eq facet_field
+      expect(helper.facet_by_field_name('b')).to eq facet_field
     end
   end