CODEWITHSUNDEEP
ruby-on-rails
Brandon
Brandon

Reputation: 95

How to validate a belongs_to field's model field

Consider the following two models

class Book < ActiveRecord::Base
  has_many :book_reports
  enum genre: [:fiction, :nonfiction]
end

class BookReport < ActiveRecord::Base
  belongs_to :book
end

I want to validate book_reports so that it only saves those with a genre of :fiction. I can add a before_save hook to check the book association's genre but am curious if there is a better way.

Upvotes: 1

Views: 669

Answers (2)

Manoel M. Neto
Manoel M. Neto

Reputation: 666

You could use custom methods:

validate :belongs_to_fiction_book, on: [:create, :update]

def belongs_to_fiction_book
    errors.add(:book, "is not a fiction book.") unless book.genre == "fiction"
end

Upvotes: 2

Danodemo
Danodemo

Reputation: 59

You could possibly use before_create callback instead so that you can catch the genre a little sooner in the workflow, but otherwise your idea is fairly sound:

Use a call-back to trigger a check on the genre, and if it doesn't match what you're looking for, reject the record and move on.

You could also use the :validates call-back to validate that self.genre == 'Fiction' or whatever else you want to check for, and use before_validation to catch it even sooner.

I recommend reading through the RubyGuides page on Active Record Callbacks to understand a bit more about the workflow, and then use best judgement to decide when to actually check the Genre value you want.

Upvotes: 1

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