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

user_313483 0
Viewed 31073

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 string. So something like:

class Interface < ActiveRecord::Base
  attr_accessible :name, :json

  validates :name,  :presence => true,
                    :length   => { :minimum => 3,
                                   :maximum => 40 },
                    :uniqueness => true

  validates :json, :presence => true,
                   :type => json #SOMETHING LIKE THIS
                   :contains => json #OR THIS    
end

How do I do that?

validation ruby-on-rails json
7 Answers

If you don't fancy enterprise-style validators or monkey-patching the String class here's a simple solution:

class Model < ApplicationRecord
  validate :json_field_format

  def parsed_json_field
    JSON.parse(json_field)
  end

  private

  def json_field_format
    return if json_field.blank?
    begin
      parsed_json_field
    rescue JSON::ParserError => e
      errors[:json_field] << "is not valid JSON" 
    end
  end
end
user_27718890

The most simple and elegant way, imo. The top upvoted answers will either return true when passing a string containing integers or floats, or throw an error in this case.

def valid_json?(string)
    hash = Oj.load(string)
    hash.is_a?(Hash) || hash.is_a?(Array)
rescue Oj::ParseError
    false
end
user_53625240
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