How to eager load a fields_for with validation - ruby-on-rails

Question

I have this fields_for in my form:
= f.fields_for :parts do |builder|
= builder.input :body, label: builder.object.another_relation.description, required: false
In the main model I have this validation:
validates_associated :parts
In the parts model I have this validation:
validates :body, presence: true
This works well. When I leave some part empty and try to create the model, the form is re-displayed again with proper error messages.
But in the logs I see that the label is querying the database for each part, so I need to eager load this.
How?
This was my try:
= f.fields_for :parts, f.object.parts.includes(:question_part) do |builder|
= builder.input :body, label: builder.object.another_relation.description, required: false
This eager loads the relationship successfully, but when I leave some field empty and try to create the model, the form is re-displayed with all parts empty and no errors. I think this is normal, as I'm forcing the fields_for to load fields from that collection I'm passing.
Anyone knows how to solve this?

Answer 1

Here's a way to do it.
Imagine these 4 models, related to a question-answers site like StackOverflow, so everyone knows what we are talking about :)
So, a question has N parts, and also N answers. While an answer belongs to a question, and has N parts. Finally, an answer part belongs to a question part.
class Question
has_many :parts, class_name: 'QuestionPart', dependent: :destroy
accepts_nested_attributes_for :parts, allow_destroy: true
has_many :answers, dependent: :destroy
# ...
end
class QuestionPart
belongs_to :question
# ...
end
class Answer
belongs_to :question
belongs_to :user
has_many :parts, class_name: 'AnswerPart', dependent: :destroy
accepts_nested_attributes_for :parts, allow_destroy: true
# ...
end
class AnswerPart
belongs_to :answer
belongs_to :question_part
validates :body, presence: true
# ...
end
Let's take a look at the answer controller:
class AnswersController < ApplicationController
def new
#question = Question.find(params[:question_id)
#answer = #question.answers.new
#question.parts.each { |p| #answer.parts.build(question_part: p) }
end
def edit
#answer = Answer.find(params[:id])
#answer_parts = #answer.parts.includes(:question_part)
end
def create
#question = Question.find(params[:question_id])
#answer = current_user.answers.build(answer_params.merge(question: #question))
if #answer.save
redirect_to #question, notice: 'The answer was successfully created.'
else
render :new
end
end
def update
##answer = Answer.find(params[:id])
#answer = Answer.where(id: params[:id]).includes(parts: [:question_part]).first
if #answer.update(answer_params)
redirect_to #answer.question, notice: 'The answer was successfully updated.'
else
render :edit
end
end
private
def answer_params
params.require(:answer).permit(:body, parts_attributes: [:id, :question_part_id, :body])
end
end
Please notice how I retrieve the answer in the update method. I have commented out the standard way, while I'm retrieving it with a custom query (which should be moved into the Answer model). Here is where I had trouble. If anyone knows a better way, just comment or add a new answer.
Now for the templates:
# new.html.erb
...
<%= form_for [#question, #answer] do |f|
<%= render 'form', f: f, parts: #answer.parts
<% end %>
# edit.html.erb
...
<%= form_for [#answer] do |f|
<%= render 'form', f: f, parts: #answer_parts || #answer.parts
<% end %>
# _form.html.erb
...
<%= f.fields_for :parts, parts do |builder| %>
<%= builder.text_field :body, label: builder.object.question_part.description, required: false
<%= builder.hidden_field :question_part_id %>
<% end %>