This is a very very naive and simple thing but I quite lost my time on this so I thought might be helpful.
Recently I was using the ‘nested_form’ gem by the great Ryan Bates (https://github.com/ryanb/nested_form). The form to create a new form works like a real gem without any effort.
Now, when I clicked on ‘edit’ link, it created some issues as the nested models didnt come.
I had a simple thing like each question has many answers. When I created a question, I added 5 answers to it but when I edited the question, no answers were visible.
The simple solution for this would be that the <% f.fields_for :answers do |an| %> line in your form would be without an equal to sign so just add it.
Thus, it looks like
<%= f.fields_for :answers do |an| %>
Thats all and it works like a charm!
Hope it helps.