class ActiveRecord::ImmutableRelation - activerecord-4.2.3 Documentation

# class ActiveRecord::ImmutableRelation

Raised when a relation cannot be mutated because it's already loaded.

    class Task < ActiveRecord::Base
    end

    relation = Task.all
    relation.loaded? # => true

    # Methods which try to mutate a loaded relation fail.
    relation.where!(title: 'TODO')  # => ActiveRecord::ImmutableRelation
    relation.limit!(5)              # => ActiveRecord::ImmutableRelation