Validation failed Class must exist

Question

I have been (hours) trouble with associations in Rails. I found a lot of similar problems, but I couldn\'t apply for my case:

City\'s class:

class Ci         


        

Answer 1

belongs_to :city, required: false

Answer 2

You need to add the following to the end of the belongs_to relationship statement:

optional: true

It is possible to set this on a global level so that it works in the same way as older versions of rails, but I would recommend taking the time to manually add it to the relationships that really need it as this will cause less pain in the future.

Answer 3

Rails.application.config.active_record.belongs_to_required_by_default = false

This works because the Rails 5 has true by default to disable you go under Initilizers then click on the New_frame-work and turn the true to false

Answer 4

This comes a bit late but this is how to turn off this by default in rails 5:

config/initializers/new_framework_defaults.rb

Rails.application.config.active_record.belongs_to_required_by_default = false

In case you don't want to add optional: true to all your belongs_to.

I hope this helps!

Answer 5

Rails 5

If you have a belongs_to relationship to :parent then you have to pass an existing parent object or create a new one then assign to children object.

Answer 6

I found out a solution to the problem "Validation failed: Class must exist" and it's better than use:

belongs_to :city, optional: true

4.1.2.11 :optional

If you set the :optional option to true, then the presence of the associated object won't be validated. By default, this option is set to false.

cause you still make a validation in application level. I solve the problem making my own validation in create method and changing user_params method:

def create

  @city = City.find(params[:city_id])

  Rails.logger.debug user_params.inspect
  @user = User.new(user_params)

  @user.city_id = @city.id

  if @user.save!
    flash[:success] = "Works!"
    redirect_to '/index'
  else
    render 'new'
  end
end

def user_params
  params.require(:user).permit(:name)
end

I didn't test this code, but it works in another project mine. I hope it can help others!