Allow plays to be scoped by album

app/controllers/plays_controller.rb

@@ -1,4 +1,6 @@
 class PlaysController < ApplicationController
+  has_scope :by_album, as: 'album_id'
+
   def index
     authorize Play
     @plays = apply_scopes(policy_scope(Play))

app/models/play.rb

@@ -12,4 +12,6 @@ class Play < ApplicationRecord
   belongs_to :user
 
   validates :played_at, presence: true
+
+  scope :by_album, ->(album) { joins(:track).where(track: { album_id: album }) }
 end

test/controllers/plays_controller_test.rb

@@ -15,6 +15,16 @@ class PlaysControllerTest < ActionDispatch::IntegrationTest
     assert_empty body
   end
 
+  test 'should get index with album scope' do
+    play1 = create(:play, track: @track, user: @user)
+    play2 = create(:play, user: @user)
+    get plays_url(album_id: @track.album_id)
+    assert_response :success
+    body = JSON.parse response.body
+    assert_includes body, play1.as_json
+    assert_not_includes body, play2.as_json
+  end
+
   test 'should create play' do
     assert_difference('Play.count', 1) do
       post plays_url, params: { play: { played_at: DateTime.current, track_id: @track.id } }

test/models/play_test.rb

@@ -10,4 +10,9 @@
 require 'test_helper'
 
 class PlayTest < ActiveSupport::TestCase
+  test 'should be able to filter by album' do
+    @play = create(:play)
+    assert_includes Play.by_album(@play.track.album_id), @play
+    assert_empty Play.by_album(@play.track.album_id + 1)
+  end
 end