accepts_nested_attributes_for issue in Form - ruby-on-rails

Question

Before asking this, I have already tried with the solution detailed here, but it didn't work.
context: 2 models, Idea and Project. 1 idea belongs to 1 project, 1 projects has many ideas.
I want to create a form to create ideas that have fields of ideas but also to specify which Project they belong to, by indicating the project_id field. I'm doing it with accepts_nested_attributes_for
Issue: I'm not being able to grab the project_id when creating a new idea from a form. From the console I see that a new idea has been saved, but project_id for that idea always returns nil
code:
ideas_controller.rb
# GET /ideas/new
def new
#idea = Idea.new
#idea.build_project
respond_to do |format|
format.html # new.html.erb
format.json { render json: #idea }
end
models> idea.rb
class Idea < ActiveRecord::Base
belongs_to :project
accepts_nested_attributes_for :project
mount_uploader :picture, PictureUploader
validates :name, presence: true, allow_blank: false
end
_form.html.erb
<%= form_for(#idea) do |f| %>
<% f.fields_for :project do |project_fields| %>
<% if #idea.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(#idea.errors.count, "error") %> prohibited this idea from being saved: </h2>
<ul>
<% #idea.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :name %><br>
<%= f.text_field :name %>
</div>
<div class="field">
<%= f.label :description %><br>
<%= f.text_area :description %>
</div>
<div class="field">
<%= f.label :picture %><br>
<%= f.file_field :picture %>
</div>
<div class="field">
<%= f.label :project %><br>
<%= f.number_field :project_id, :class=>"Number" %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
<% end %>

Answer 1

"Nested attributes allow you to save attributes on associated records through the parent", according to the documentation. you are doing it through the child, which I don't think is possible.
So either move the accepts_nested_attributes_for to the parent model and use the parent's form to create the parent fields along with the child field. so you'll be creating project and idea through the projects_controller and projects/_form.html.erb
or opt out for something else.
without using accepts_nested_attributes_for, add project_ids to your ideas params attributes as an empty array:
def idea_params
params.require(:idea).permit(:name, :project_ids => [])
end
app/views/ideas/_form.html.erb:
<div>
<%= idea.label 'File under at least one project' %>
<% Project.all.order(name: :asc).each do |project| %>
<div>
<%= check_box_tag "idea[project_ids][]", project.id %>
<%= project.name %>
</div>
</div>
this code will give you checkboxes of your projects to select. this means first you have to create the projects separely in project's own controller and form. so you are not using nesting attributes.