Rails Client side Collection Validation fails - Simple Form

Question

I have to build a simple app that allows users to loan and borrow books. Simply put a User can create books, and they can pick another user to loan the book to.

I have three models User, Book and Loan:

class User < ActiveRecord::Base
  devise :database_authenticatable, :registerable,
     :recoverable, :rememberable, :trackable, :validatable

  has_many :books
  has_many :loans, through: :books
  has_many :borrowings, class_name: "Loan"

  validates :username, uniqueness: true
  validates :username, presence: true
end

class Book < ActiveRecord::Base
  belongs_to :user
  has_many :loans

  validates :title, :author, presence: true
end

class Loan < ActiveRecord::Base
  belongs_to :user
  belongs_to :book

  validates :user, :book, :status, presence: true
end

The LoansController looks like this:

class LoansController < ApplicationController
  before_action :find_book, only: [:new, :create]

  def new
    @users = User.all
    @loan = Loan.new
    authorize @loan
  end

  def create
    @loan = Loan.new
    @loan.book = @book
    @loan.user = User.find(loan_params[:user_id])
    @loan.status = "loaned"
    authorize @loan
    if @loan.save
      redirect_to :root
    else
      render :new
    end
  end

  private

  def loan_params
    params.require(:loan).permit(:user_id)
  end

  def find_book
    @book = Book.find(params[:book_id])
  end
end

My form looks like:

<%= simple_form_for([@book, @loan]) do |f| %>
  <%= f.input :user_id, collection: @users.map { |user| [user.username, user.id] }, prompt: "Select a User" %>
  <%= f.submit %>
<% end %>

If I submit the form without selecting a user, and keep the "Select a User" prompt option, the form is submitted and the app crash because it can't find a user with id=

I don't know why the user presence validation in the form does not work...

Answer 1

you will change your Create method

  def create
    @loan = Loan.new
    @loan.book = @book
    @loan.user = User.find_by_id(loan_params[:user_id])
    @loan.status = "loaned"
    authorize @loan
    if @loan.save
      redirect_to :root
    else
      render :new
    end
  end