Allow for per-action resources (#99)

Sometimes you want `index` powered by ElasticSearch but `show` is a
normal ActiveRecord Resource. While we still support the existing
syntax, you can now pass a hash of per-action Resources:

```ruby
class PostsController < ApplicationController
  jsonapi resource: {
    index: PostSearchResource,
    show: PostResource
  }
end
```

Author: richmolj

lib/jsonapi_compliable/base.rb

@@ -106,7 +106,14 @@ def sideload_whitelist
     #
     # @return [Resource] the configured Resource for this controller
     def jsonapi_resource
-      @jsonapi_resource ||= self.class._jsonapi_compliable.new
+      @jsonapi_resource ||= begin
+        resource = self.class._jsonapi_compliable
+        if resource.is_a?(Hash)
+          resource[action_name.to_sym].new
+        else
+          resource.new
+        end
+      end
     end
 
     # Instantiates the relevant Query object

spec/integration/rails/finders_spec.rb

@@ -131,6 +131,11 @@ class AuthorResource < JsonapiCompliable::Resource
       def index
         render_jsonapi(Author.all)
       end
+
+      def show
+        scope = jsonapi_scope(Author.all)
+        render_jsonapi(scope.resolve.first, scope: false)
+      end
     end
 
     let!(:author1) { Author.create!(first_name: 'Stephen', dwelling: house, state: state, organization: org1) }
@@ -203,6 +208,33 @@ def json
       end
     end
 
+    context 'when action-specific resources' do
+      before do
+        klass = Class.new(JsonapiCompliable::Resource) do
+          type :authors
+          use_adapter JsonapiCompliable::Adapters::ActiveRecord
+        end
+
+        controller.class.jsonapi resource: {
+          index: Integration::AuthorResource,
+          show: klass
+        }
+      end
+
+      it 'uses the correct resource for each action' do
+        get :index, params: { include: 'books' }
+        expect(json_includes('books').length).to eq(2)
+        controller.instance_variable_set(:@jsonapi_resource, nil)
+        expect {
+          if Rails::VERSION::MAJOR >= 5
+            get :show, params: { id: author1.id, include: 'books' }
+          else
+            get :show, id: author1.id, params: { include: 'books' }
+          end
+        }.to raise_error(JsonapiCompliable::Errors::InvalidInclude)
+      end
+    end
+
     context 'sideloading has_many' do
       # TODO: may want to blow up here, only for index action
       it 'allows pagination of sideloaded resource' do