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

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