Why ActiveRecord automatically validates has_many association

Question

Following models are given:

class Question < ActiveRecord::Base
  has_many  :answers
end

class Answers < ActiveRecord::Base
  belongs_to: question
  validates :comment, presence: true
end

When calling

question = Question.new
question.answers.build
question.valid?

valid? returns false because the associated answer is not valid. When writing

has_many :answers, validate: false

in Question valid?returns true.

Is it a bug or is it desired when using has_many the associated models are validated automatically? The Rails Guides explicitly explain the use of validate_associated with a has_many relationship: http://guides.rubyonrails.org/active_record_validations_callbacks.html#validates_associated

Answer 1

It's most definitely not a bug.

• You've created a Question
• You've told Rails to attach a new instance of Answer and relate it to this new Question
• You're then asking "Rails, is this Question/Answer model and association I've created ready to be saved to the database?"

As you've found, Rails will say "No" in your case.

I have never used and do not care about validates_associated. I can however point you to documentation explaining why you're seeing the behavior you are.

• Active Record Autosave Association

Though the documentation at the above source file is worth reading in it's entirety, I'll pull out this bit for you

Note that :autosave => false is not same as not declaring :autosave. When the :autosave option is not present new associations are saved.

• You have not specified :autosave => SOMETHING on your :answers association
• Because of this, Rails by default is going to try and save your newly build/associated Answer on your new Question
• The save will fail because the Answer is invalid