ActiveAdmin::Resource loads resources for breadcrumbs

Closes activeadmin#2266

Add `ActiveAdmin::Resource#find_resource`. This is now a centralized place to
load a resource, with correct handling of primary key, decoration, etc.

Then, use this new way of loading resources in the Breadcrumbs logic.
This was the original impetus for for defining
`ActiveAdmin::Resource#find_resource`. Previously, the `BreadcrumbsHelper`
did a one-off load of the resource, which has historically been a source of
bugs and/or inconsistencies.

Please note that this is duplication with InheritedResources. Normally, the
resource is loaded by InheritedResources, but there are situations in which
ActiveAdmin needs to load resources as well (ie Breadcrumbs). It was not
reasonable to use InheritedResources to load the resource (see the discussion
at activeadmin#2315).

Author: amiel

lib/active_admin/resource.rb

@@ -135,6 +135,11 @@ def csv_builder
       @csv_builder || default_csv_builder
     end
 
+    def find_resource(id)
+      resource = resource_class.where(resource_class.primary_key => id).first
+      decorator_class ? decorator_class.new(resource) : resource
+    end
+
     # @deprecated
     def resource
       resource_class

lib/active_admin/view_helpers/breadcrumb_helper.rb

@@ -13,8 +13,7 @@ def breadcrumb_links(path = request.path)
           # 3. default to calling `titlecase` on the URL fragment
           if part =~ /\A(\d+|[a-f0-9]{24})\z/ && parts[index-1]
             config = active_admin_config.belongs_to_config.try(:target) || active_admin_config
-            obj    = config.resource_class.where( config.resource_class.primary_key => part ).first
-            name   = display_name obj
+            name   = display_name config.find_resource(part)
           end
           name ||= I18n.t "activerecord.models.#{part.singularize}", :count => 1.1, :default => part.titlecase
 

spec/unit/resource_spec.rb

@@ -208,5 +208,36 @@ def config(options = {})
         end
       end
     end
+
+    describe '#find_resource' do
+      let(:resource) { namespace.register(Post) }
+      let(:post) { stub }
+      before do
+        Post.stub(:where).with('id' => '12345').and_return { [post] }
+      end
+
+      it 'can find the resource' do
+        resource.find_resource('12345').should == post
+      end
+
+      context 'with a decorator' do
+        let(:resource) { namespace.register(Post) { decorate_with PostDecorator } }
+        it 'decorates the resource' do
+          resource.find_resource('12345').should == PostDecorator.new(post)
+        end
+      end
+
+      context 'when using a nonstandard primary key' do
+        let(:different_post) { stub }
+        before do
+          Post.stub(:primary_key).and_return 'something_else'
+          Post.stub(:where).with('something_else' => '55555').and_return { [different_post] }
+        end
+
+        it 'can find the post by the custom primary key' do
+          resource.find_resource('55555').should == different_post
+        end
+      end
+    end
   end
 end

spec/unit/view_helpers/breadcrumbs_spec.rb

@@ -11,16 +11,20 @@ def params; {}; end
     # Mock link to and return a hash
     def link_to(name, url); {:name => name, :path => url}; end
 
+    let(:post) { mock(:display_name => 'Hello World') }
+
+    let(:post_config) { stub(find_resource: post) }
+
     let :active_admin_config do
-      m = mock
-      m.stub_chain(:belongs_to_config, :target, :resource_class).and_return Post
-      m
+      active_admin_config = stub
+      active_admin_config.stub_chain(:belongs_to_config, :target).and_return post_config
+      active_admin_config
     end
 
     let(:trail) { breadcrumb_links(path) }
 
     context "when request '/admin'" do
-      let(:path){ "/admin" }
+      let(:path) { "/admin" }
 
       it "should not have any items" do
         trail.size.should == 0
@@ -71,16 +75,14 @@ def link_to(name, url); {:name => name, :path => url}; end
       end
 
       context "when Post.find(1) doesn't exist" do
+        before { post_config.stub(find_resource: nil) }
         it "should have a link to /admin/posts/1" do
           trail[2][:name].should == "1"
           trail[2][:path].should == "/admin/posts/1"
         end
       end
 
       context "when Post.find(1) does exist" do
-        before do
-          Post.stub(:where).with('id' => '1').and_return{ [ mock(:display_name => 'Hello World') ] }
-        end
         it "should have a link to /admin/posts/1 using display name" do
           trail[2][:name].should == "Hello World"
           trail[2][:path].should == "/admin/posts/1"
@@ -104,6 +106,7 @@ def link_to(name, url); {:name => name, :path => url}; end
       end
 
       context "when Post.find(4e24d6249ccf967313000000) doesn't exist" do
+        before { post_config.stub(find_resource: nil) }
         it "should have a link to /admin/posts/4e24d6249ccf967313000000" do
           trail[2][:name].should == "4e24d6249ccf967313000000"
           trail[2][:path].should == "/admin/posts/4e24d6249ccf967313000000"
@@ -112,7 +115,7 @@ def link_to(name, url); {:name => name, :path => url}; end
 
       context "when Post.find(4e24d6249ccf967313000000) does exist" do
         before do
-          Post.stub(:where).with('id' => '4e24d6249ccf967313000000').and_return{ [ mock(:display_name => 'Hello :)') ] }
+          post_config.stub(:find_resource => mock(:display_name => 'Hello :)'))
         end
         it "should have a link to /admin/posts/4e24d6249ccf967313000000 using display name" do
           trail[2][:name].should == "Hello :)"
@@ -136,7 +139,7 @@ def link_to(name, url); {:name => name, :path => url}; end
         trail[1][:path].should == "/admin/posts"
       end
       it "should have a link to /admin/posts/1" do
-        trail[2][:name].should == "1"
+        trail[2][:name].should == "Hello World"
         trail[2][:path].should == "/admin/posts/1"
       end
       it "should have a link to /admin/posts/1/comments" do
@@ -145,17 +148,5 @@ def link_to(name, url); {:name => name, :path => url}; end
       end
     end
 
-    context 'when using a nonstandard primary key' do
-      let(:path) { '/admin/posts/55555/comments' }
-      before do
-        Post.stub(:primary_key).and_return 'something_else'
-        Post.stub(:where).with('something_else' => '55555').and_return{ [ mock(:display_name => 'Hello Hello!') ] }
-      end
-      it 'should link to /admin/posts/55555 using display name' do
-        trail[2][:name].should == 'Hello Hello!'
-        trail[2][:path].should == '/admin/posts/55555'
-      end
-    end
-
   end
 end