Improve queries for serializers

app/helpers/injection_helper.rb

@@ -1,6 +1,8 @@
 require 'open_food_network/enterprise_injection_data'
 
 module InjectionHelper
+  include SerializerHelper
+
   def inject_enterprises(enterprises = Enterprise.activated.includes(address: :state).all)
     inject_json_ams(
       'enterprises',
@@ -11,9 +13,11 @@ module InjectionHelper
   end
 
   def inject_enterprise_shopfront_list
+    select_only = required_attributes Enterprise, Api::EnterpriseShopfrontListSerializer
+
     inject_json_ams(
       'enterprises',
-      Enterprise.activated.includes(address: :state).all,
+      Enterprise.activated.select(select_only).includes(address: :state).all,
       Api::EnterpriseShopfrontListSerializer
     )
   end

app/helpers/serializer_helper.rb

@@ -3,4 +3,13 @@ module SerializerHelper
     return [] if ids.blank?
     ids.map { |id| { id: id } }
   end
+
+  # Returns an array of the fields a serializer needs from it's object
+  # so we can #select only what the serializer will actually use
+  def required_attributes(model, serializer)
+    model_attributes = model.attribute_names
+    serializer_attributes = serializer._attributes.keys.map(&:to_s)
+
+    (serializer_attributes & model_attributes).map { |attr| "#{model.table_name}.#{attr}" }
+  end
 end

app/serializers/api/enterprise_shopfront_list_serializer.rb

@@ -2,7 +2,8 @@
 module Api
   class EnterpriseShopfrontListSerializer < ActiveModel::Serializer
     attributes :name, :id, :latitude, :longitude, :is_primary_producer, :is_distributor,
-               :visible, :path, :icon, :icon_font, :producer_icon_font
+               :visible, :path, :icon, :icon_font, :producer_icon_font, :address_id, :sells,
+               :permalink
 
     has_one :address, serializer: Api::AddressSerializer
 

spec/helpers/serializer_helper_spec.rb

@@ -0,0 +1,18 @@
+require 'spec_helper'
+
+describe SerializerHelper, type: :helper do
+  let(:serializer) do
+    class ExampleEnterpriseSerializer < ActiveModel::Serializer
+      attributes :id, :name
+    end
+    ExampleEnterpriseSerializer
+  end
+
+  describe "#required_attributes" do
+    it "returns only the attributes from the model that the serializer needs to be queried" do
+      required_attributes = helper.required_attributes Enterprise, serializer
+
+      expect(required_attributes).to eq ['enterprises.id', 'enterprises.name']
+    end
+  end
+end