It has to be defined like this
scope :recent, order_by(:created_at => :desc).limit(100)
You can check out the mongoid documentation for scopes here
From the page
Named scopes are defined at the class level using a scope macro and can be chained to create result sets in a nice DSL.
class Person
include Mongoid::Document
field :occupation, type: String
field :age, type: Integer
scope :rock_n_rolla, where(occupation: "Rockstar")
scope :washed_up, where(:age.gt => 30)
scope :over, ->(limit) { where(:age.gt => limit) }
end
# Find all the rockstars.
Person.rock_n_rolla
# Find all rockstars that should probably quit.
Person.washed_up.rock_n_rolla
# Find a criteria with Keith Richards in it.
Person.rock_n_rolla.over(60)