Question

I’m looking at the fb_graph api gem and it has some code in the migration https://github.com/nov/fb_graph_sample/blob/master/db/migrate/20110623075710_create_subscriptions.rb I can’t figure out, namely, for the column type, it has belongs_to, which is not a typical column type.

class CreateSubscriptions < ActiveRecord::Migration
  def self.up
    create_table :subscriptions do |t|
      t.belongs_to :facebook
      t.string :object, :fields, :verify_token
      t.text :history_json
      t.timestamps
    end
  end

  def self.down
    drop_table :subscriptions
  end
end

I understand the belongs_to has_many associations in Rails as they’re usually used, but they never require a column of the type belongs_to and I wouldn’t expect a database to accept that type of column.

Also, in the model https://github.com/nov/fb_graph_sample/blob/master/app/models/subscription.rb the belongs_to Facebook is declared but I don’t get how the database column is actually used. Can anyone explain?

class Subscription < ActiveRecord::Base
  belongs_to :facebook

  validates :facebook, :object, :fields, :history_json, :verify_token, :presence => true

  before_validation :setup, :on => :create

  def history
    JSON.parse(self.history_json)
  end

  def history=(history)
    self.history_json = history.to_json
  end

  def subscribe!(callback)
    Facebook.app.subscribe!(
      :object => self.object,
      :fields => self.fields,
      :callback_url => callback,
      :verify_token => self.verify_token
    )
  end

  private

  def setup
    self.verify_token = ActiveSupport::SecureRandom.hex(16)
    self.history = []
  end

end

Here’s a link to the Facebook.rb model https://github.com/nov/fb_graph_sample/blob/master/app/models/facebook.rb

Facebook.rb

class Facebook < ActiveRecord::Base
  has_many :subscriptions

  def profile
    @profile ||= FbGraph::User.me(self.access_token).fetch
  end

  class << self
    extend ActiveSupport::Memoizable

    def config
      @config ||= if ENV['fb_client_id'] && ENV['fb_client_secret'] && ENV['fb_scope'] && ENV['fb_canvas_url']
        {
          :client_id     => ENV['fb_client_id'],
          :client_secret => ENV['fb_client_secret'],
          :scope         => ENV['fb_scope'],
          :canvas_url    => ENV['fb_canvas_url']
        }
      else
        YAML.load_file("#{Rails.root}/config/facebook.yml")[Rails.env].symbolize_keys
      end
    rescue Errno::ENOENT => e
      raise StandardError.new("config/facebook.yml could not be loaded.")
    end

    def app
      FbGraph::Application.new config[:client_id], :secret => config[:client_secret]
    end

    def auth(redirect_uri = nil)
      FbGraph::Auth.new config[:client_id], config[:client_secret], :redirect_uri => redirect_uri
    end

    def identify(fb_user)
      _fb_user_ = find_or_initialize_by_identifier(fb_user.identifier.try(:to_s))
      _fb_user_.access_token = fb_user.access_token.access_token
      _fb_user_.save!
      _fb_user_
    end
  end

end

Answer 1

There are many questions in you one question, the one about belongs_to, you will find an answer here: t.belongs_to in migration.