CODEWITHSUNDEEP
ruby-on-railsactiverecordmodel
cmaughan
cmaughan

Reputation: 2634

validate at least one in has_and_belongs_to_many

I have a model with:

has_and_belongs_to_many :users

How do I validate that the model has at least one user in the model? I tried:

validates_presence_of :users

But that doesn't seem to give me what I want...

Upvotes: 26

Views: 12501

Answers (5)

Jakub Troszok
Jakub Troszok

Reputation: 103863

I would write custom validation:

validate :has_users?

def has_users?
  # rails 2:
  errors.add_to_base "Model must have some users." if self.users.blank?
end

That would do exactly that.

Note in rails 3+ you have to use:

  # rails 3+
  errors.add :base, "Model must have some users." if self.users.blank?

In rails 4+ there's a built-in shortcut, so you can simply do:

validates :users, presence: true

Upvotes: 36

Guihen
Guihen

Reputation: 135

Try:

validates :users, :length => { :minimum => 1 }

Upvotes: 1

Jaco Pretorius
Jaco Pretorius

Reputation: 24830

In rails 4 you can just do

validates :users, presence: true

Upvotes: 33

Wojtek B.
Wojtek B.

Reputation: 927

In Rails 3.2.x:

validate :has_users?

def has_users?
  errors.add(:base, 'Error message') if self.users.blank?
end

Upvotes: 3

John Topley
John Topley

Reputation: 115432

Josh Susser wrote a plugin that adds a validates_existence_of method that does what you want. It ensures that a foreign key references a record that exists.

Upvotes: 1

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