Eager-load the user feed to avoid repetitive queries

app/models/user.rb

@@ -83,6 +83,7 @@ def feed
                      WHERE  follower_id = :user_id"
     Micropost.where("user_id IN (#{following_ids})
                      OR user_id = :user_id", user_id: id)
+             .includes(:user, image_attachment: :blob)
   end
 
   # Follows a user.

test/integration/microposts_interface_test.rb

@@ -2,10 +2,35 @@
 
 class MicropostsInterfaceTest < ActionDispatch::IntegrationTest
 
+  class QueryCountHandler
+    attr_reader :count
+
+    def initialize
+      @count = 0
+    end
+
+    def call(name, started, finished, unique_id, payload)
+      # puts payload[:sql]
+      @count += 1
+    end
+  end
+
   def setup
     @user = users(:michael)
   end
 
+  def count_sql(message)
+    warn "Counting SQL queries for: #{message}"
+
+    count_handler = QueryCountHandler.new
+    ActiveSupport::Notifications.subscribe 'sql.active_record', count_handler
+
+    yield
+
+    warn "Observed #{count_handler.count} SQL queries"
+    ActiveSupport::Notifications.unsubscribe count_handler
+  end
+
   test "micropost interface" do
     log_in_as(@user)
     get root_path
@@ -18,12 +43,18 @@ def setup
     # Valid submission
     content = "This micropost really ties the room together"
     image = fixture_file_upload('kitten.jpg', 'image/jpeg')
+
     assert_difference 'Micropost.count', 1 do
-      post microposts_path, params: { micropost: { content: content,
-                                                   image:   image } }
+      count_sql 'Create a valid post' do
+        post microposts_path, params: { micropost: { content: content,
+                                                    image:   image } }
+      end
+      assert assigns(:micropost).image.attached?
+    end
+
+    count_sql 'Follow redirect after posting' do
+      follow_redirect!
     end
-    assert assigns(:micropost).image.attached?
-    follow_redirect!
     assert_match content, response.body
     # Delete a post.
     assert_select 'a', 'delete'