Passing hash as values in hidden_field_tag

Question

I am trying to pass some filters in my params through a form like so:

hidden_field_tag "filters", params[:filters]

For some reason the params get changed in the next page. For example, if params[:filters] used to be...

"filters"=>{"name_like_any"=>["apple"]} [1]

...it gets changed to...

"filters"=>"{\"name_like_any\"=>[\"apple\"]}" [2]

note the extra quotations and backslashes in [2] when compared to [1].

Any ideas? I'm attempting to use this with searchlogic for some filtering, but I need it to persist when I change change objects in forms. I would prefer not to have to store it in session.

Answer 1

it's because when you convert in HTML with your hidden_field_tag, the backquote is add. After when you received it like a string not a Hash.

The Hash type can't exist in HTML. You have only string. So if you want pass your hash (not recommend by me), you need eval it when you received it. But can be a big security issue on your application.

Answer 2

You actually want/need to 'serialize' a hash using hidden fields.

Add this to your ApplicationHelper :

  def flatten_hash(hash = params, ancestor_names = [])
    flat_hash = {}
    hash.each do |k, v|
      names = Array.new(ancestor_names)
      names << k
      if v.is_a?(Hash)
        flat_hash.merge!(flatten_hash(v, names))
      else
        key = flat_hash_key(names)
        key += "[]" if v.is_a?(Array)
        flat_hash[key] = v
      end
    end

    flat_hash
  end

  def flat_hash_key(names)
    names = Array.new(names)
    name = names.shift.to_s.dup 
    names.each do |n|
      name << "[#{n}]"
    end
    name
  end

  def hash_as_hidden_fields(hash = params)
    hidden_fields = []
    flatten_hash(hash).each do |name, value|
      value = [value] if !value.is_a?(Array)
      value.each do |v|
        hidden_fields << hidden_field_tag(name, v.to_s, :id => nil)          
      end
    end

    hidden_fields.join("\n")
  end

Then, in view:

<%= hash_as_hidden_fields(:filter => params[:filter]) %>

This should do the trick, even if you have a multilevel hash/array in your filters.

Solution taken http://marklunds.com/articles/one/314