How to validate if a string is json in a Rails model

Question

I\'m building a simple app and want to be able to store json strings in a db. I have a table Interface with a column json, and I want my rails model to validate the value of the

Answer 1

Currently (Rails 3/Rails 4) I would prefer a custom validator. Also see https://gist.github.com/joost/7ee5fbcc40e377369351.

# Put this code in lib/validators/json_validator.rb
# Usage in your model:
#   validates :json_attribute, presence: true, json: true
#
# To have a detailed error use something like:
#   validates :json_attribute, presence: true, json: {message: :some_i18n_key}
# In your yaml use:
#   some_i18n_key: "detailed exception message: %{exception_message}"
class JsonValidator < ActiveModel::EachValidator

  def initialize(options)
    options.reverse_merge!(:message => :invalid)
    super(options)
  end

  def validate_each(record, attribute, value)
    value = value.strip if value.is_a?(String)
    ActiveSupport::JSON.decode(value)
  rescue MultiJson::LoadError, TypeError => exception
    record.errors.add(attribute, options[:message], exception_message: exception.message)
  end

end