ValidateJsonRecord.rb

# Example class by christophercotton to show how to validate JSON in 
# ActiveRecord

class Stuff < ActiveRecord::Base
  validates_presence_of :my_field
  validate :valid_json

  # make sure the JSON is valid
  def valid_json
    begin
      ActiveSupport::JSON.decode(my_field)
    rescue
      @errors.add(:my_field, "must contain valid JSON")
    end
  end

end