Active Record and file: How do i write Json file with my data?

Question

How do I write a data in table event to json file? Please see this code:

In model event.rb

 class Event < ActiveRecord::Base
  attr_accessible :name, :event_description, :start_at, :end_at, :status, :eventable_id
  has_event_calendar
  belongs_to :eventable, polymorphic: true
  after_save :write_json


end
def write_json
    Event.all.each do |event|
            @eventJson = {
            "id" => event.id,
            "start" => event.start_at,
            "end" => event.end_at,
            "title" => event.name,
            "body" => event.event_description,
            "status" => event.status
            } 

    end
    File.open("public/event.json","w") do |f|
      f.write(@eventJson.to_json)
    end 

 end

In file Json there's one record, but in table event there are many records. How do I write all records from table event to event.json file after saving the record?

public/event.json

{"id":35,"start":"2013-03-28T00:00:00Z","end":"2013-03-28T00:00:00Z","title":"1345edrewrewr","body":"123124","status":"Confirm"}

Answer 1

The problem is that you assign a value to @eventJson in a loop so the previous values are lost. You should use an array:

def write_json
  events_json = []
  Event.all.each do |event|
    event_json = {
      "id" => event.id,
      "start" => event.start_at,
      "end" => event.end_at,
      "title" => event.name,
      "body" => event.event_description,
      "status" => event.status
    } 
    events_json << event_json
  end
  File.open("public/event.json","w") do |f|
    f.write(events_json.to_json)
  end 
end

Answer 2

In this case, you might want to use map instead of each -- it's much cleaner. Given that you said the method is in the model, this is how it would look.

class Event < ActiveRecord::Base
    ...

    def self.write_json
      record_json = self.all.map{ |record| { self.name => record.attributes } }.to_json
      File.open("#{Rails.root}/#{(self.name.underscore)}.json", "w") do |f|
        f.write record_json
      end 
    end
end