Rails5, unpermitted params in nested form, while associating existing objects

Question

Why why why...?

Three models (FirstModel, SecondModel, JoinedModel), JoinedModel belongs to both others and other two has_many of each other, through JoinedModel. JoinedModel accepts_nested_attributes_for first_model and second_model.

It also validates presence of first_model_id and second_model_id.

Joined model strong params:

private
 def joined_params
   params.require(:joined_model).permit(:first_model_id, :second_model_id,
                  :first_models_attributes => [:id, :name],
                  :second_models_attributes => [:id, :full_name])
 end

JoinedModel's _form:

<%= form_for(joined_model) do |f| %>
 <%= f.fields_for :second_models do |ff| %>
  <%= ff.select(SecondModel.all.map {|c| [ c.full_name, c.id ] }, { include_blank: true }) -%>

(and the same f.fields_for for FirstModel)

When I submit this form, I get

Unpermitted params first_models, second_models

And query:

Parameters: {"utf8"=>"✓", "authenticity_token"=>"gvW/OrOXJruAK0ZD+uoajJ4N+dZvpmZF8Ay0TOKF9HPO19d4tRBoWz0C4VoaOABYat8KzrryL8lp5ax+Y9ZJRg==", "joined_model"=>{"first_models"=>{"first_model_id"=>"1"}, "second_models"=>{"second_model_id"=>"1"}}, "commit"=>"Create Joined model"}

I dont know why, how etc. form tries to send a hash - "second_models"=>{"second_model_id"=>"1"} it supposed to be just like "second_model_id"=>"1" and it does like this if my form uses simple f.number_field :first_model_id instead of select...

You should add an answer with your answer, then accept it. Feels weird, but is absolutely acceptable (and encouraged)! Also, maybe think about a title with more clarity? How can we help others find this solution when they have this problem? — coreyward
yes, good idea, i will post it. About the title, I thought its even better like this - many relevant keywords (could't think any others :))) ) — Julius
Your title should be a concise, relevant question or problem statement. Search works plenty well without keyword loading. ;) — coreyward
Hm, maybe yes, time has come when machines became smarter... I will fix it :) thx — Julius

Julius Julius · Accepted Answer · 2017-03-16T13:20:32

I found the answer and will leave this post, since many similar unanswered questions found on StackOverflow

So, the answer was to use parent's fields builder for select, like:

<%= form_for(joined_model) do |f| %>
 <%= f.fields_for :second_models do |ff| %>
  <%= f.select(SecondModel.all.map {|c| [ c.full_name, c.id ] }, { include_blank: true }) -%>

Looks like it works all fine now, but if anyone knows why I even need to provide builder object (in my case |ff|) for nested fields if I am not even using it, I will give a Hi Five and a Tango dance!

UPDATE:

So I found that in this situation I didn't even needed fields_for... Now it all makes sence, since here I was creating a new JoinedModel's record and only selecting other two (existing) records and association simply lets me grab those methods... Bit lame, but oh well...

Rails5, unpermitted params in nested form, while associating existing objects

1 Answers