optimize pluck

spec/loading_optimizations_spec.rb

@@ -6,12 +6,16 @@ require "spec_helper"
 RSpec.describe "loading optimizations" do
   context "cars table" do
     before do
-      Car.create!(name: "Toyota Camry", fuel_type: "gasoline")
-      Car.create!(name: "Toyota Prius", fuel_type: "hybrid")
-      Car.create!(name: "Toyota Corolla", fuel_type: "electric")
+      Car.create!(name: "Toyota Camry", fuel_type: "gasoline", engine_size: 2.0)
+      Car.create!(name: "Toyota Prius", fuel_type: "hybrid", engine_size: 1.5)
+      Car.create!(
+        name: "Toyota Corolla",
+        fuel_type: "electric",
+        engine_size: 1.8
+      )
     end
 
-    it "queries only the aux table if plucking values that are on the aux table" do
+    it "queries only the aux table if no main table columns are referenced" do
       queries =
         SpecHelper.capture_queries do
           expect(Car.pluck(:fuel_type)).to eq(%w[gasoline hybrid electric])
@@ -21,6 +25,21 @@ RSpec.describe "loading optimizations" do
       expect(queries.first).not_to include("JOIN")
     end
 
+    it "queries only the aux table if all columns are on the aux table" do
+      queries =
+        SpecHelper.capture_queries do
+          expect(Car.where(engine_size: 1.4..1.9).pluck(:fuel_type)).to eq(
+            %w[hybrid electric]
+          )
+        end
+
+      expect(queries.length).to eq(1)
+      expect(queries.first).not_to include("JOIN")
+      expect(queries.first).to include("BETWEEN")
+      expect(queries.first).to match(/\bvehicles_car_aux\b/)
+      expect(queries.first).not_to match(/\bvehicles\b/)
+    end
+
     it "queries both tables if main table column is referenced" do
       queries =
         SpecHelper.capture_queries do