Rule #2 to validate belongs_to association for presence

Andrei Kaleshka

13 Jul 2013

Recently I’ve resolved one more problem which concerns presence validator and belongs_to association. But it’s involved another thing - accepts_nested_attributes. Assume you have nested form and parent object is not exist yet, so you can have this issue. Here I will show you how to fix it.

Issue

Let’s we have the following models and their relations:

class Account
  has_one :user
  accepts_nested_attributes_for :user
end

class User
  belongs_to :account
  validates :account, :presence => true
end

Go to rails console and check the validator out:

irb(main):001:0> params = {:account => {:user_attributes => {}}}
irb(main):002:0> a = Account.new(params[:account])
irb(main):003:0> a.valid? # => false
irb(main):004:0> a.errors.full_messages # => ["User account can't be blank"]

So this is an our challenge - we can’t save account, because user can’t pass validation rules because account (parent model) is not existed yet! But to remove validator won’t be right solution. Are you agree with me?

Solution

A solution for this issue is very simple - just add to has_one (or if you have has_many) one more option - :inverse_of. With this option rails won’t try to get account from database when user is validated. The account will be got from memory. If you don’t familiar with this option I strongly recommend you to read an official rails guide.

So, change account model try it:

class Account
  has_one :user, :inverse_of => :account
  accepts_nested_attributes_for :user
end

irb(main):001:0> params = {:account => {:user_attributes => {}}}
irb(main):002:0> a = Account.new(params[:account])
irb(main):003:0> a.valid? # => true

I hope this article was helpful for you.