Question

If you supply Mongo with a hash that uses symbols as keys and save the document, it will ‘stringify’ it, meaning the keys will be converted to strings. To summarize:

condition:                       hash keys will be:
----------                       ------------------
after initializing a document    symbols or strings
after saving a document          strings
after fetching a document        strings

This ‘asymmetry’ has led to some ugliness in my tests. I would like to be able to ‘rely on’ the keys always being strings – and not worry about if the document has just been initialized or not.

What are one or more elegant ways to avoid this?

Note: In my case, I’m using Mongoid, but I don’t think this question is necessarily Mongoid specific. It probably applies to any Rails project that uses MongoDB.

Answer 1

Something along these lines could work. Basically this code redefines Mongoid’s field macro (its setter).

require 'mongoid'

module Stringifier
  def field name, args = {}
    super # call mongoid implementation

    define_method "#{name}=" do |val|
      val.stringify_keys! if val && val.respond_to?(:stringify_keys!)
      super(val)
    end
  end
end

class Foo
  include Mongoid::Document
  extend Stringifier

  field :subhash, type: Hash
end

f = Foo.new
f.subhash = {a: 1, b: 2}

puts f.subhash
# >> {"a"=>1, "b"=>2}

This may not be the cleanest implementation, but you get the idea.