Support composite IDs

Rails 7 supports composite primary keys, which means we need to pull the ID param with `extract_value`.

lib/implicit_resource.rb

@@ -35,7 +35,7 @@ def collection
 
   def resource
     @resource ||= if params[:id].present?
-      collection.find(params[:id])
+      collection.find(primary_key)
     else
       collection.new
     end
@@ -64,4 +64,12 @@ def act_on_resource
       end
     end
   end
+
+  def primary_key
+    if model_klass.primary_key.is_a?(Array)
+      params.try(:extract_value, :id)
+    else
+      params[:id]
+    end
+  end
 end

test/controllers/posts_controller_test.rb

@@ -0,0 +1,13 @@
+require "test_helper"
+require "json"
+
+class PostssControllerTest < ActionDispatch::IntegrationTest
+  test "show action returns the correct post" do
+    get post_url(posts(:composite_key)), headers: { "Accept" => "application/json" }
+    json_response = JSON.parse(@response.body)
+
+    assert_equal posts(:composite_key).author_id, json_response["author_id"]
+    assert_equal posts(:composite_key).slug, json_response["slug"]
+    assert_response :success
+  end
+end

test/dummy/app/controllers/posts_controller.rb

@@ -0,0 +1,9 @@
+class PostsController < ApplicationController
+  include ImplicitResource
+
+  private
+
+  def permitted_attributes(_resource)
+    params.require(:post).permit(:author_id, :slug)
+  end
+end

test/dummy/app/models/post.rb

@@ -0,0 +1,2 @@
+class Post < ApplicationRecord
+end

test/dummy/config/routes.rb

@@ -9,4 +9,5 @@
   # root "posts#index"
 
   resources :articles
+  resources :posts
 end

test/dummy/db/migrate/20240421044857_create_posts.rb

@@ -0,0 +1,10 @@
+class CreatePosts < ActiveRecord::Migration[7.1]
+  def change
+    create_table :posts, primary_key: [:author_id, :slug] do |t|
+      t.integer :author_id
+      t.string  :slug,
+
+      t.timestamps
+    end
+  end
+end

test/dummy/db/schema.rb

@@ -10,12 +10,20 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.1].define(version: 2024_03_29_195908) do
+ActiveRecord::Schema[7.1].define(version: 2024_04_21_044857) do
   create_table "articles", force: :cascade do |t|
     t.string "title", null: false
     t.text "body", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
   end
 
+  create_table "posts", primary_key: ["author_id", "slug"], force: :cascade do |t|
+    t.integer "author_id"
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.string "slug"
+    t.string "#<ActiveRecord::ConnectionAdapters::SQLite3::TableDefinition:0x0000ffff9de4e240>"
+  end
+
 end

test/fixtures/posts.yml

@@ -0,0 +1,3 @@
+composite_key:
+  author_id: 1
+  slug:      my-post-title