```ruby
# frozen_string_literal: true
class InstanceUser < ActiveRecord::Base
  include InstanceUserSearchConcern
  acts_as_tenant :instance, inverse_of: :instance_users

  enum role: { normal: 0, instructor: 1, administrator: 2, auto_grader: 3 }
  belongs_to :user, inverse_of: :instance_users

  scope :ordered_by_username, -> { joins(:user).merge(User.order(name: :asc)) }

  def self.search_and_ordered_by_username(keyword)
    keyword.blank? ? ordered_by_username : search(keyword).group('users.name').ordered_by_username
  end
end
```

Remove auto_grader role from instance user.
user
```ruby
# frozen_string_literal: true
class InstanceUser < ActiveRecord::Base
  include InstanceUserSearchConcern
  acts_as_tenant :instance, inverse_of: :instance_users

  enum role: { normal: 0, instructor: 1, administrator: 2 }
  belongs_to :user, inverse_of: :instance_users

  scope :ordered_by_username, -> { joins(:user).merge(User.order(name: :asc)) }

  def self.search_and_ordered_by_username(keyword)
    keyword.blank? ? ordered_by_username : search(keyword).group('users.name').ordered_by_username
  end
end
```
assistant