Simpleform, create two nested models at once

Question

I have two models that are nested, a Project has a name and a Budget, and a Budget has an amount and belongs to a Project.

I got a form page where I try to create both Project and Budget, so users can fill the name of their project in the same form where they choose the budget amount.

<%= simple_form_for @project do |f| %>
    <%= f.error_notification %>
    <%= simple_fields_for :budget do |ff| %>
      <%= ff.input :amount %>
    <% end %>
    <%= f.input :name %>
    <%= f.submit "Create", class: "btn" %>
  <% end %>

But I can't create both at the same time, when I test if my budget is valid, I miss the project_id it is linked to, and if I try to create my project first, I can't cause it misses its budget.

Here are my models :

 class Budget < ApplicationRecord
   belongs_to :projects
 end
 class Project < ApplicationRecord
   has_one :budget
   accepts_nested_attributes_for :budget
 end

Here are my migrations

class CreateBudgets < ActiveRecord::Migration[5.1]
  def change
    create_table :budgets do |t|

      t.timestamps
    end
  end
end
class CreateProjects < ActiveRecord::Migration[5.1]
  def change
    create_table :projects do |t|
      t.references :budget, foreign_key: true
      t.string :name

      t.timestamps
    end
  end
end

Finaly here is my controller for project def new @project = Project.new @project.id = 0 @budget = Budget.new puts "new in projectcontroler" end

def create
  puts "create in projectcontroler"
  # Getting filled objects from form
  @project = Project.new(project_params)
  @budget = Budget.new(budget_params)
  puts "We're on project controller"
  p @budget

  respond_to do |format|
    unless @budget.nil? 
      @project.budget = @budget

      if @project.valid?
        puts "All good now"
        @budget.save
        @project.save
        puts "Campaign successfuly created"
        format.html { redirect_to projects_path, notice: 'Success' }
      else
        puts "Unable to create campaign"
        format.html { render :new, notice: 'Project went wrong' }
      end

     else # If budget isn't saved
      puts "Unable to create budget"
      @budget.errors.full_messages.each do |mes|
        puts mes
      end
      format.html { render :new }
      format.json { render json: @budget.errors, status: :unprocessable_entity }
    end
  end
end

For now I got this issue : ActiveModel::MissingAttributeError - can't write unknown attribute project_id

I need to understand if I need to have a controller or routes for budget model, can't I create both models in this same controller ?

EDIT : Updated code

EDIT 2 : I add migrations as I think it's part of the problem

class CreateProjects < ActiveRecord::Migration[5.1]
  def change
    create_table :projects do |t|
      t.references :budget, foreign_key: true
      t.string :name
      t.timestamps
    end
  end
end
class CreateBudgets < ActiveRecord::Migration[5.1]
  def change
    create_table :budgets do |t|
      t.string :amount
      t.timestamps
    end
  end
end

Answer 1

You need to use accepts_nested_attributes_for here. It allows you to save attributes on associated records through the parent.

class Project < ApplicationRecord
   has_one :budget
   accepts_nested_attributes_for :budget
end

In this case you need a standard routes and a form for a project: <%= simple_form_for @project do |f| %>

In params you'll get a hash budget_attributes: {} inside project_params, so you don't need to create a budget separately.

And you need to change your migrations. If your Budget really belongs_to to the Project, then budgets table need to store project_id, and you have vice versa.

Controller

def new
  @project = Project.new
end

def create
  @project = Project.new(project_params)


  respond_to do |format|
    if @project.save
      format.html { redirect_to projects_path, notice: 'Success' }
    else
      format.html { render :new, notice: 'Project went wrong' }
    end
  end
end

private
def project_params
  params.require(:project).permit(budget_attributes: [:id, :name])
end

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