Question

I’m having an issue with passing the generated JSON notation of my object to my Sinatra application. The problem I have is twofold:

• I have 2 classes that are mapped to a database using the Sequel gem. When they generate JSON it is ok and properly implemented.
• I have a custom class called registration that maps one of the classes with an additional field. The goal is to generate JSON out of this and pass that JSON to the application using cucumber (test purpose)

The application code responsible for handling the request has the following function defined:

post '/users' do
  begin
    hash = JSON.parse(self.request.body.read)
    registration = Registration.new.from_json(@request.body.read)
    registration.user.country = Database::Alaplaya.get_country_by_iso_code(registration.user.country.iso_code)
    return 400 unless(registration.is_valid?)
    id = Database::Alaplaya.create_user(registration.user)

    # If the registration failed in our system, return a page 400.
    return 400 if id < 1
end

• problem 1: I cannot use the params hash. It exists but is just an empty hash. Why?
• problem 2: I cannot deserialize the JSON generated by the class itself. Why?

The registration class looks like this:

require 'json'

class Registration
  attr_accessor :user, :project_id

  def to_json(*a)
    {
        'json_class'   => self.class.name,
        'data'         => [@user.to_json(*a), @project_id]
    }.to_json(*a)
  end

  def self.json_create(o)
    new(*o['data'])
  end

  # Creates a new instance of the class using the information provided in the
  # hash. If a field is missing in the hash, nil will be assigned to that field
  # instead.
  def initialize(params = {})
    @user = params[:user]
    @project_id = params[:project_id]
  end

  # Returns a string representing the entire Registration.
  def inspect
    "#{@user.inspect} - #{@user.country.inspect} - #{@project_id}"
  end

  # Returns a boolean valid representing whether the Registration instance is
  # considered valid for the API or not. True if the instance is considered
  # valid; otherwise false.
  def is_valid?
    return false if @user.nil? || @project_id.nil?
    return false if !@user.is_a?(User) || !@project_id.is_a?(Fixnum)
    return false if !@user.is_valid?
    true
  end
end

I had to implement the methods to generate the JSON output correctly. When I run this in console I get the following output generated:

irb(main):004:0> r = Registration.new(:user => u, :project_id => 1)
=> new_login - nil - 1
irb(main):005:0> r.to_json
=> "{\"json_class\":\"Registration\",\"data\":[\"{\\\"json_class\\\":\\\"User\\\
",\\\"login\\\":\\\"new_login\\\"}\",1]}"

Which looks like valid JSON to me. However when I POST this to the application server and try to parse this, JSON complains that at least 2 octets are needed and refuses to deserialize the object.

Answer 1

If you’re using Sequel as your ORM, try something like this:

In your model:

class Registration < Sequel::Model
  many_to_one :user
  many_to_one :project
  plugin :json_serializer
end        

The server:

before do
  @data = JSON.parse(request.body.read) rescue {}
end

post '/users' do
  @registration = Registration.new @data
  if @registration.valid?
    @registration.save 
    @registration.to_json #return a JSON representation of the resource
  else
    status 422 #proper status code for invalid input
    @registration.errors.to_json
  end
end

I think you may be overcomplicating your registration process. If the HTTP action is POST /users then why not create a user? Seems like creating a registration is overly complex. Unless your user already exists, in which case POST /users would be incorrect. If what you’re really intending to do is add a user to to a project, then you should PUT /projects/:project_id/users/:user_id and the action would look something like this:

class User < Sequel::Model
  many_to_many :projects
end
class Project < Sequel::Model
  many_to_many :users
end
#make sure your db schema has a table called users_projects or projects_users

put '/projects/:project_id/users/:user_id' do
  #find the project
  @project = Project.find params[:project_id]
  raise Sinatra::NotFound unless @project
  #find the user
  @user = Project.find params[:project_id]
  raise Sinatra::NotFound unless @user
  #add user to project's users collection
  @project.add_user @user
  #send a new representation of the parent resource back to the client
  #i like to include the child resources as well
  #json might look something like this
  #{ 'name' : 'a project name', 'users' : ['/users/:user_id', '/users/:another_user_id'] }
  @project.to_json
end