Question

I am trying to query a db that uses a join to find users that require an alert. My query works fine in the model it is written for and it also works through the scope when the parameter being passed is explicit. However when I pass the parameter as a variable it does not work. Here is my code:

class Alert < ActiveRecord::Base
  belongs_to :user
  attr_accessible :first_alert, :second_alert, :third_alert, :user_id
  def self.find_users_to_alert(time)
    where(:third_alert => time)
  end
  scope :alerter, find_users_to_alert (here is where i want to pass param)
end

class User < ActiveRecord::Base
  has_many :alerts
  attr_accessor :password
  attr_accessible :name, :email, :password, :password_confirmation

  scope :alerts_to_be_sent, joins(:alerts) & Alert.alerter
end

The error I am getting is a NameError undefined local variable or method. But I would have thought passing the value of the variable in the rails console like:

User.alerts_to_be_sent(5)

would be ok. Help would be appreciated thanks.

Answer 1

From the Active Record Query Interface Guide:

Using a class method is the preferred way to accept arguments for scopes. These methods will still be accessible on the association objects […]

So write class methods instead:

class Alert < ActiveRecord::Base
  def self.alerter(t)
    find_users_to_alert(t)
  end
end

def User < ActiveRecord::Base
  def self.alerts_to_be_sent(t)
    joins(:alerts) & Alert.alerter(t)
  end
end