How to render template to a variable in Padrino?

Question

I'm trying to implement a nested form in Padrino where I can add multiple instances of the child object using a Add whatever button in the interface.

In Rails, one method to do this is to create a helper that generates nested fields everytime you click that Add whatever button:

def link_to_add_fields( text, f, association, target )

  new_object    = f.object.class.reflect_on_association(association).klass.new
  template_path = "#{association}/fields" 

  template = f.fields_for(association, new_object) do |builder|
    render(template_path, :f => builder)
  end

  link_to text, "#", onclick: "add_#{association}_fields(this, \"#{escape_javascript(template)}\", \"#{target}\")"

end

However, when I try to do this in Padrino the f.fields_for (...) block doesn't render to the template variable, but instead is displayed in the layout.

I'm trying to find something like render_to_string or similar in Padrino framework.

Anyone knows how to solve this? Thanks

Answer 1

It's not render that's failing you, it's fields_for. It erroneously detects that it's called from your erb template and concats to it.

Inherently it's true because you call link_to_add_fields from your erb, but at the time there is no detection method to guess this double dive from erb to ruby and back.

It can be considered a bug and you could create an issue here https://github.com/padrino/padrino-framework and provide a minimal failing project with a locked Gemfile.

As a solution I can suggest you manually switch your rendering engine to ruby and back like this:

  def my_rendery_helper
     @current_engine, engine_was = nil, @current_engine
     template = fields_for(:moo) do |builder|
       render('moo')
     end
     @current_engine = engine_was
     template # now contains a SafeBuffer string
     'result'
  end

@current_engine is a class variable that is used to detect rendering engine internally.