Rails - Validate Presence Of Association?

Question

I have a model A that has a \"has_many\" association to another model B. I have a business requirement that an insert into A requires at least 1 associated record to B. Is

Answer 1

You can validate associations with validates_existence_of (which is a plugin):

Example snippet from this blog entry:

class Tagging < ActiveRecord::Base
  belongs_to :tag
  belongs_to :taggable, :polymorphic => true
  validates_existence_of :tag, :taggable

  belongs_to :user
  validates_existence_of :user, :allow_nil => true
end

Alternatively, you can use validates_associated. As Faisal notes in the comments below the answer, validates_associated checks if the associated object is valid by running the associated class validations. It does not check for the presence. It's also important to note that a nil association is considered valid.