Preprocessing conditionals in erb

Question

I want to DRY the code as much as I can, but I think this maybe too dry..

I have a fields_for partial, that sometimes I need to have it by relation and sometimes fields_for for the object itself

<%= form_for model_name do |f| %>


 <%= render partial: 'fields_for_partial', locals: {f: f, ... } %>

<% end %>

calling the fields_for partial would be different depending on when I need the form - if I want to create a new model I would use the form_for's f, but sometimes I want to edit the model and just show a particular nested model, which then I would use fields_for nil, obj to render the fields for that specific object

I attempted to do this when testing a local variable f that I am passing

<% if f.nil? %>
    <%= fields_for object_name, obj do |ff| %>
<% else %>
    <%= f.fields_for object_name, obj do |ff| %>
<% end %>

the rest of the partial would be a regular fields_for with ff like

which is obviously a massive fail..

How would I write this kind of code?

Answer 1

You can use local_assigns:

<% form_or_view = local_assigns[:f] || self %>
<%= form_or_view.fields_for object_name, obj do |ff| %>

Answer 2

move the call to fields_for outside of the shared partial. Take for example a project and a task. You allow users to create a project and a task at the same time.

# using HAML
# project form
= form_for @project do |f|
  = f.fields_for :tasks do |tf|
    = render 'tasks/form', f: tf

You also allow users to create only tasks.

# task form
= form_for @task do |f|
  = render 'tasks/form', f: f

The tasks/_form.html.haml partial will look like

# task fields
= f.text_field :title
= f.text_area :description