From 323ef31d281edef8b5e8ab9096f3a8450fa6d648 Mon Sep 17 00:00:00 2001
From: Rob Di Marco <rob@elocal.com>
Date: Fri, 13 Apr 2018 17:07:59 -0400
Subject: [PATCH] Spec to illustrate error thrown when including fast_jsonapi

When trying to use the fast_jsonapi gem, we started getting an exception in unrelated `ActiveRecord` code like:

```
 Failure/Error:
   def #{name}_id
     association(:#{name}).reader.try(:id)

 NoMethodError:
   undefined method `has_scope?' for nil:NilClass
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/reflection.rb:872:in `has_scope?'
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/reflection.rb:873:in `has_scope?'
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/associations/association.rb:288:in `skip_statement_cache?'
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/associations/singular_association.rb:39:in `find_target'
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/associations/association.rb:157:in `load_target'
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/associations/association.rb:53:in `reload'
 # ./vendor/bundle/ruby/2.4.0/gems/activerecord-5.1.6/lib/active_record/associations/singular_association.rb:7:in `reader'
 # ./lib/extensions/has_one.rb:15:in `city_id'

```

This error was only showing when we had required in the `fast_jsonapi` and was happening in code that was not doing JSON serialization.

The reason for the error was that we were making a call to an `ActiveRecord` `select` where we were explicitly selecting the ID value for a `has_one` that was coming through another relation.

The `HasOne` monkey patch in `lib/extensions/has_one.rb` is the cause of this error.

The spec above illustrates the problem. If you run it, you will see the above exception. If you comment out the code in `lib/extensions/has_one.rb`, you will see the new spec passes.
---
 spec/lib/extensions/active_record_spec.rb | 67 +++++++++++++++++++++++
 1 file changed, 67 insertions(+)

diff --git a/spec/lib/extensions/active_record_spec.rb b/spec/lib/extensions/active_record_spec.rb
index e31ffe78..ac45f9ad 100644
--- a/spec/lib/extensions/active_record_spec.rb
+++ b/spec/lib/extensions/active_record_spec.rb
@@ -24,16 +24,50 @@
         supplier_id int,
         FOREIGN KEY (supplier_id) REFERENCES suppliers(id)
       );
+
+      create table cities (
+        name varchar(30),
+        id int primary key
+      );
+
+      create table zip_codes (
+        code varchar(5),
+        id int primary key,
+        primary_city_id int,
+        FOREIGN KEY (primary_city_id) REFERENCES cities(id)
+      );
+
+      create table locations (
+        zip_code_id int,
+        city_id int,
+        id int primary key,
+        is_primary int,
+        FOREIGN KEY (city_id) REFERENCES cities(id),
+        FOREIGN KEY (zip_code_id) REFERENCES zip_codes(id)
+      );
+
+      create table object_with_cities (
+        zip_code_id int,
+        id int primary key,
+        FOREIGN KEY (zip_code_id) REFERENCES zip_codes(id)
+      );
     SQL
 
     # Insert records
     @account_id = 2
     @supplier_id = 1
     @supplier_id_without_account = 3
+    @city_id = 1
+    @zip_code_id = 1
     db.execute_batch <<-SQL
       insert into suppliers values ('Supplier1', #{@supplier_id}),
                                    ('SupplierWithoutAccount', #{@supplier_id_without_account});
       insert into accounts values ('Dollar Account', #{@account_id}, #{@supplier_id});
+
+      insert into cities values ('Beverly Hills', #{@city_id});
+      insert into zip_codes values ('90210', #{@zip_code_id}, #{@city_id});
+      insert into locations values (#{@zip_code_id}, #{@city_id}, 1, 1);
+      insert into object_with_cities values (#{@zip_code_id}, 1);
     SQL
   end
 
@@ -47,12 +81,45 @@ class Account < ActiveRecord::Base
       belongs_to :supplier
     end
 
+    class Location < ActiveRecord::Base
+      belongs_to :zip_code
+      belongs_to :city
+      scope :primary, -> { where(is_primary: 1) }
+    end
+
+    class ZipCode < ActiveRecord::Base
+      # has_one :primary_loc, -> { where(is_primary: 1) }, class_name: 'Location'
+      has_many :locations
+      # has_many :cities, through: :locations
+    end
+
+    class City < ActiveRecord::Base
+      has_many :locations
+      has_many :zip_codes, through: :locations
+    end
+
+    class ObjectWithCity < ActiveRecord::Base
+      belongs_to :zip_code
+
+      has_one :primary_loc, class_name: 'Location', through: :zip_code
+      has_one :city, class_name: 'City', through: :primary_loc
+    end
+
     ActiveRecord::Base.establish_connection(
       :adapter => 'sqlite3',
       :database  => @db_file
     )
   end
 
+  context 'with a belongs with a different foreign key' do
+    it 'can serialize the results' do
+      obj = ObjectWithCity.group('cities.id').select('cities.id city_id').joins(zip_code: { locations: :city }).first
+
+      # Commenting out the code in lib/extensions/has_one.rb will make this pass
+      expect(obj.city_id).to be_present
+    end
+  end
+
   context 'has one patch' do
 
     it 'has account_id method for a supplier' do