Question

How do I perform validations checks (and insert error messages into an errors structure) on an attribute which is has_one association.

If an error has occured in “shirt” or “pants”, how can i access that error?
Will the error be in person.shirt.errors[:color] ?

When i trigger person.save, are validations for person.shirt activated?

When i trigger person.save and there is an error in person.shirt, where will the error message be saved? In person.shirt.errors or in person.errors?

class Person < ActiveRecord::Base
      has_one   : shirt
      has_many  : pants
      validates :name, :presence => true
      validates_length_of :name, :minimum => 3
end

person = Person.new(:name => "JD")
person.shirt.create(:color=> "red")
person.pants.create(:type=> "jeans")
person.valid?

Answer 1

You can validate an association of the model with

validates_associated :shirt

That way when you call person.save it will trigger the validations of shirt.

And yes, you can access the association’s error with person.shirt.errors but be sure to do that after triggering validations. For example:

person = Person.new
person.errors # => will be empty

This is because validations haven’t been ran yet. So you need to call either save or valid? or any other method that triggers validations.

person = Person.new
person.valid?
person.errors # => will have errors in person

And it’s the same for the associations:

person.shirt.valid?
person.shirt.errors

but since you’re validating the associations with validates_associated it will be enough with person.valid? to trigger shirt’s validations.