Question

In my Rails app I have Users. Users are asked for their home city and district / neighborhood.

class User < ActiveRecord::Base
  belongs_to :city
  belongs_to :district
end

class City < ActiveRecord::Base
  has_many :users
  has_many :districts
end

class District < ActiveRecord::Base
  has_many :users
  belongs_to :city
end

In forms I build the associations using a virtual attribute on the User model that accepts a string (more info below in case it’s relevant).

In the console this all works great, but in the UI it’s not working. The problem seems to be, I can get city_name through a form no problem, but when I try to assign city and district in the same form it always fails. In other words, mass assignment doesn’t work.

@user.update_attributes(params[:user])

Instead the only thing I have been able to figure out is to manually set each key from a form submission, like:

@user.name = params[:user][:name] if params[:user][:name]
@user.city_name = params[:user][:city_name] if params[:user][:city_name]
@user.district_name = params[:user][:district_name] if params[:user][:district_name]

This approach works, but it’s a pain, kind of brittle, and feels all wrong because it starts gunking the controller up with a lot of logic.

My question is:

1. Is there a way to create or update attributes in a specific order, ideally in the model so that the controller doesn’t have to worry about all this?

2. Am I doing this wrong? If so, what approach would be better.

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Extra Info

Here’s how I build the associations using virtual attributes on the user model, in case that’s relevant to any potential answerers:

I want users to be able to select a city by just typing in a name, like “Chicago, IL”. This works fine, using a virtual attribute on the user model like so:

def city_name
  city.try :full_name
end

def city_name=(string)
  self.city = City.find_or_create_by_location_string( string )
end

It only makes sense for a user to find or create a district from the city they’ve chosen. This works slightly differently:

def district_name
  district.try :name
end

def district_name=(string)
  if self.city.nil?
    raise "Cannot assign a district without first assigning a city."
  else
    self.district = self.city.districts.find_or_create_by_name( string )
  end
end

In the model layer these things work fine, as long as both a city_name and district_name are set the district association works as expected.

Answer 1

I think you could do a few things to clean this up. First, you can use delegates to clean up the code. e.g.

delegate :name, :to => :city, :prefix => true, :allow_nil => true

that way you can do something like

user = User.create
user.city_name # nil
city = City.create(:name => 'chicago')
user.city = city
user.save
user.city_name # chicago

and it will just work.

Next, I would say take the name-to-id logic out of your model. You can do it either in the form (e.g. an ajax search puts the district id/city id into a hidden field), or in the controller. Then just assign the city/district as normal.