Friday, 16 January 2015

Testing the ActiveRecord models using Rspec

Usually the skeleton of my models spec looks like this:

require 'spec_helper'
                        
describe Car do
                        
  context 'class hierarchy' do
    #Here comes the class hierarchy specification
  end
                        
  context 'fields' do
  end
                        
  context 'assotiations' do
    #Here comes the enumeration of associations
  end
                        
  context 'validations' do
    #Here comes the validation of models
  end
                        
  context 'callbacks' do
    #Specs for callbacks
  end
                        
  context 'methods' do
  end
end

Testing the class hierarchy:
Since the model could include modules which affect the functionality I consider it necessary to assert on them.

describe Car do
  context 'class hierarchy' do
    specify {expect(subject.class).to be < ActiveRecord::Base}
    specify{expect(subject).to be_kind_of(Elasticsearch::Model)}
    specify{expect(subject).to be_kind_of(Elasticsearch::Model::Callbacks)}
  end
end

Testing the fields:
I often encountered errors when the model was expected to have a field and that field was missing. So I always assert on the used fields:

describe Car do
  context 'fields' do
    specify {expect(subject).to respond_to(:name)}
    specify {expect(subject).to respond_to(:filter)}
  end
end

Testing the associations:
I test the presence of the correct associations using the 'shoulda-matchers' gem.

describe Car do
  context 'assotiations' do
    specify { expect(subject).to belong_to(:user) }
    specify { expect(subject).to belong_to(:manufacturer) }
  end
end

Testing the validations:
I usually test the validations of the fields using the 'shoulda-matchers' gem.

describe Car do
  context 'validations' do
    specify { expect(subject).to validate_uniqueness_of(:filter).scoped_to(:manufacturer_id)}
  end
end

Testing the callbacks:
My callback test usually are like this:

describe Car do
  context 'validations' do
    context 'before_destroy' do
      specify 'call destroy like callback'do
        expect(equipment).to receive(:destroy_likes)
        equipment.destroy
      end
    end
  end
end

Testing the methods:
Usually I test the methods by calling it the asserting that all the necessary changes are made. I do this for all the execution paths.


Thursday, 15 January 2015

Api Development in Ruby On Rails

Recently I wrote a series of blog posts about the best practices of API development in RoR and how to develop API in general.

Let me summarize those posts:


Happy API development :)

API development in Rails error path


In my series of of API development I haven't covered the error handling.

Let me share my experience with you about what I have learned about proper error handling.
I call error path the case when the user can't achieve what he wants.

This case can happen by the following reasons:

  • The user calls an invalid url
  • The user addresses a missing resource
  • The user misses a mandatory parameter
  • The uses passes a wrong parameter
  • Some other internal error occurs
  • ...

Since thousands of calls can be made daily or hourly against the API there is no way to stop the server and debug it. So all the information related to the erroneous call must be recorded. Basically all the information to reproduce the error must be recorded. I call this ApiCallAudit.

Such an ApiCallAudit must contain:

  • All the incoming parameters
  • The type of call (GET, POST, DELETE, ...)
  • cookies
  • backtrace
  • created_at
I added some additional fields to it for filtering purposes:

  • level. It serves to quickly determine the possible source of errors. It could be parameter_error, unexpected_error, parameter_missing_error, entity_missing_error
  • status. It is a default error message.
  • code. An error code which uniquely identifies the error.
In the beginning the error code was missing from my design and the mobile clients were using the default error message. This has some disadvantages:
  • The mobile UI is usually developed in a different codebase. And the server side error message modification is not possible. Specially if the same chunk of server side code is serving many applications.
  • -The language used on the mobile UI can vary. For example the UX developer can decide to use:
    1. "You haven't provided the group" - First person complaining style.
    2. "The group is missing" - Passive objective style
    3. "Please provide a group" - Proactive gentle style
    4. "Select a group!" - Imperative style
    5. ...
In order to formulate the sentences which reflects the application mood the mobile developer needs to interpret the returned error based on its error_code and formulate its own corresponding message.

Happy coding :)



API Development Restfull vs Facebook style


In the last months I developed mainly API's using grape gem and their related gems.

In this blog post I will express my opinion how to organise the API which manages the entities.

Generally speaking I like the REST concept and I organize my API to conform that way. For cases when there are no association among the entities this philosophy is good enough and clear.

However I like the API to reflect the associations when we are dealing with has_many or has_and_belongs_to_many associations. Just like in case of  Facebook Graph API. In these cases I find that style more intuitive and I am following that style whenever I deal with associations.

Examples:

Lets suppose that cars and manufacturers can be reviewed.

class Car < ActiveRecord::Base
  has_many :reviews, as: :reviewable

class Manufacturer < ActiveRecord::Base
  has_many :reviews, as: :reviewable

class Review < ActiveRecord::Base
  belongs_to :user
  belongs_to :reviewable, polymorphic: true

In this case the review API would be:
  • creation of reviews:
    POST /api/cars/{id}/reviews
    POST /api/manufacturers/{id}/reviews
  • retrieval of reviews:
    GET /api/cars/{id}/reviews
    GET /api/manufacturers/{id}/reviews
  • deletion of reviews:
    DELETE /api/reviews/{id}


In the classic restful style the review creation would be:

    params do
      requires :comment, type: String, desc: "The comment"
      requires :reviewable_id, type: Integer, desc: "The id of a reviewable entity"
      requires :reviewable_type, type: String, desc: "The type of a reviewable entity"
    end
    POST /api/reviews

Both solutions have pros and cons. The restful style is more DRY. The Facebook Graph Api style relieves more information about the associations ergo it is more intuitive and easier to use.

Happy coding :)