Rails not saving nested attributes - ruby-on-rails

Question

I have the tables Task and Item. I have a form for Item where I record all the possible items that my Tasks may have, which is working fine. Then I have the form for Task where all the Items are displayed alongside a field to put a cost value for each item. This will result in a join between Task and Item: TaskItem (this table contains task_id, item_id and cost).
When I submit the form, it's saving the Task but not the TaskItems associated. I don't see what I'm missing as I searched a lot for this problem and nothing seems to work. Please, see the code below.
Model:
class Task < ApplicationRecord
has_many :task_items
has_many :items, :through => :task_items
accepts_nested_attributes_for :task_items, :allow_destroy => true
end
class Item < ApplicationRecord
has_many :task_items
has_many :tasks, :through => :task_items
end
class TaskItem < ApplicationRecord
belongs_to :task
belongs_to :item
accepts_nested_attributes_for :item, :allow_destroy => true
end
Controller:
def new
#items = Item.all
#task = Task.new
#task.task_items.build
end
def create
#task = Task.new(task_params)
#task.save
redirect_to action: "index"
end
private def task_params
params.require(:task).permit(:id, :title, task_items_attributes: [:id, :item_id, :cost])
end
My view:
<%= form_for :task, url:tasks_path do |f| %>
<p>
<%= f.label :title %><br>
<%= f.text_field(:title, {:class => 'form-control'}) %><br>
</p>
<% #items.each do |item| %>
<% #task_items = TaskItem.new %>
<%= f.fields_for :task_items do |ti| %>
<%= ti.label item.description %>
<%= ti.text_field :cost %>
<%= ti.hidden_field :item_id, value: item.id %>
<% end %>
<% end %>
<p>
<%= f.submit({:class => 'btn btn-primary'}) %>
</p>

Answer 1

You need to add inverse_of option to the has_many method in class Task:
class Task < ApplicationRecord
has_many :task_items, inverse_of: :task
has_many :items, through: :task_items
accepts_nested_attributes_for :task_items, :allow_destroy => true
end
This is due to the when creating a new TaskItem instance, it requires that the Task instance already exists in database to be able to grab the id fo the Task instance. Using this option, it skips the validation.
You can read this post about inverse_of option and its use cases.
fields_for has an option to specify the object which is going to store the information. This combined with building each of the TaskItem from the has_many collection should ensure that all the relationship are set correctly.
View Code:
<%= form_for #task do |f| %>
<p>
<%= f.label :title %><br>
<%= f.text_field(:title, {:class => 'form-control'}) %><br>
</p>
<% #items.each do |item| %>
<% task_item = #task.task_items.build %>
<%= f.fields_for :task_items, task_item do |ti| %>
<%= ti.label item.description %>
<%= ti.text_field :cost %>
<%= ti.hidden_field :item_id, value: item.id %>
<% end %>
<% end %>
<p>
<%= f.submit({:class => 'btn btn-primary'}) %>
</p>
<% end %>
Controller Code:
def index
end
def new
#items = Item.all
#task = Task.new
end
def create
#task = Task.new(task_params)
#task.save
redirect_to action: "index"
end
private
def task_params
params.require(:task).permit(:id, :title, task_items_attributes: [:id, :item_id, :cost])
end