```ruby
# == Schema Information
#
# Table name: schedule_items
#
#  id          :integer          not null, primary key
#  title       :string(255)
#  excerpt     :text
#  description :text
#  start_time  :datetime
#  duration    :integer
#  event_id    :integer
#  room_id     :integer
#  created_at  :datetime
#  updated_at  :datetime
#

class ScheduleItem < ActiveRecord::Base

  attr_accessible :title,
                  :description,
                  :excerpt,
                  :start_time,
                  :duration,
                  :room_id,
                  ad: :admin

  # Associations
  belongs_to :event
  belongs_to :room

  # Provides #overlaps?
  include ScheduleOverlapsMixin

  # Public attributes for export
  include PublicAttributesMixin
  set_public_attributes :id, :title, :excerpt, :description, :start_time, :end_time, :duration,
    :event_id, :event_title,
    :room_id, :room_title,
    :created_at, :updated_at

  # Return the time this session ends.
  def end_time
    if self.start_time
      self.start_time + (self.duration || 0).minutes
    else
      nil
    end
  end

  #---[ Accessors for getting the titles of related objects ]-------------

  def room_title
    return self.room.try(:name)
  end

  def event_title
    return self.event.try(:slug)
  end
  alias_method :event_slug, :event_title
end
```

Fix typo in ScheduleItem's attr_accessible
user
```ruby
# == Schema Information
#
# Table name: schedule_items
#
#  id          :integer          not null, primary key
#  title       :string(255)
#  excerpt     :text
#  description :text
#  start_time  :datetime
#  duration    :integer
#  event_id    :integer
#  room_id     :integer
#  created_at  :datetime
#  updated_at  :datetime
#

class ScheduleItem < ActiveRecord::Base

  attr_accessible :title,
                  :description,
                  :excerpt,
                  :start_time,
                  :duration,
                  :room_id,
                  as: :admin

  # Associations
  belongs_to :event
  belongs_to :room

  # Provides #overlaps?
  include ScheduleOverlapsMixin

  # Public attributes for export
  include PublicAttributesMixin
  set_public_attributes :id, :title, :excerpt, :description, :start_time, :end_time, :duration,
    :event_id, :event_title,
    :room_id, :room_title,
    :created_at, :updated_at

  # Return the time this session ends.
  def end_time
    if self.start_time
      self.start_time + (self.duration || 0).minutes
    else
      nil
    end
  end

  #---[ Accessors for getting the titles of related objects ]-------------

  def room_title
    return self.room.try(:name)
  end

  def event_title
    return self.event.try(:slug)
  end
  alias_method :event_slug, :event_title
end
```
assistant