DataMapper::Property::ValidatedJson

validated_json.rb

require 'dm-types'
require 'dm-validations'


module DataMapper
  module Validations
    class DeferredJsonValidator < GenericValidator
      def initialize(field_name, pending_error_ivar_name, options={})
        super(field_name, options)
        
        @pending_error_ivar_name = pending_error_ivar_name
      end
      
      def call(target)
        return true unless target.instance_variable_defined?(@pending_error_ivar_name)
        
        message = '%s is not valid JSON: %s' % [
          DataMapper::Inflector.humanize(field_name),
           target.instance_variable_get(@pending_error_ivar_name),
        ]
        
        add_error(target, message, field_name)
        
        false
      end
    end
  end
  
  class Property
    # Provides a Json-based property that defers JSON validation errors to the validation step of 
    # the model.
    # 
    # If your JSON fails to validate, the property is represented as nil
    class ValidatedJson < Json
      attr_reader :pending_error_instance_variable_name
      
      def initialize(*args)
        super
        
        @pending_error_instance_variable_name = "#{instance_variable_name}_pending_error".freeze
        
        unless model.skip_auto_validation_for?(self)
          # A more manual form of DataMapper::Validations::ClassMethods#add_validator_to_context
          validator = Validations::DeferredJsonValidator.new(name, @pending_error_instance_variable_name)
          
          context = model.validators.context(:default)
          unless context.include? validator
            context << validator
            model.send :create_context_instance_methods, :default
          end
        end
      end
      
      def set(resource, value)
        begin
          super
          # Clean up the ivar on success
          if resource.instance_variable_defined? pending_error_instance_variable_name
            resource.send(:remove_instance_variable, pending_error_instance_variable_name)
          end
          
        rescue ::JSON::ParserError => err
          resource.instance_variable_set(pending_error_instance_variable_name, err.message)
          super(resource, nil)
        end
      end
    end
  end
end