Rails Namespaced Model Not Triggering Callbacks

Question

Basic Group Model:

class Group < ActiveRecord::Base
  @@ItemType = 'GroupItem' # Base ItemType
  after_initialize :default_item_type

  has_many :group_assignments
  has_many :items, through: :group_assignments, source: :groupable, source_type: @@ItemType, dependent: :destroy

  accepts_nested_attributes_for :items, allow_destroy: true

  private
  def default_item_type
    self.item_type = @@ItemType if self.new_record?
  end
end

Namespaced Model:

class Gradation::Group < Group
  @@ItemType = 'Gradation' # Base ItemType
  after_initialize :default_item_type

  has_many :group_assignments
  has_many :items, through: :group_assignments, source: :groupable, source_type: @@ItemType, dependent: :destroy

  accepts_nested_attributes_for :items, allow_destroy: true
  private
  def default_item_type
    self.item_type = @@ItemType if self.new_record?
  end
end

I am attempting to have a field *item_type* be set on the *after_initialize* callback, but not matter what I do, the callback is only triggered on the regular group model and not the namespaced one.

I am struggling to understand why this is the expected behavior, and also how to get callbacks to work for the namespaced Group .

Answer 1

Using the class variable here @@ItemType = 'Gradation' is not likely to help you out. In an initial modeling of this problem, the @@ItemType were stepping on each other, always giving you 'Gradation'

The following will work. You'll notice the differences:

1. move to constant for the class instead of class variable
2. changed the namespacing around

app/models/group.rb

class Group < ActiveRecord::Base
  ITEM_TYPE = 'GroupItem' # Base ItemType
  after_initialize :default_item_type

  private
  def default_item_type
    self.item_type = ITEM_TYPE if self.new_record?
  end
end

app/models/group/gradation.rb

class Group::Gradation < Group
  ITEM_TYPE = 'Gradation' # Base ItemType

  private
  def default_item_type
    self.item_type = ITEM_TYPE if self.new_record?
  end
end

Notes:

1. You cannot use the SingleTableInheritance here -- Rails expects there to be a gradations table
2. you must define default_item_type on each subclass so that it can pull the correct ITEM_TYPE

To get rid of #2 above, you could do this:

class Group < ActiveRecord::Base
  ITEM_TYPE = 'GroupItem' # Base ItemType
  after_initialize :default_item_type

  private
  def default_item_type
    self.item_type = "#{self.class}::ITEM_TYPE".constantize if self.new_record?
  end
end

Then, each subclass could be:

class Group::Graduation < Group
  ITEM_TYPE = 'Graduation' # Base ItemType  
end

Answer 2

The overall solution to my problem looks like this...

Base Group Model:

class Group < ActiveRecord::Base
  @@ItemType = 'GroupItem' # Base ItemType
  after_initialize :default_item_type

  has_many :group_assignments
  has_many :items, through: :group_assignments, source: :groupable, source_type: @@ItemType, dependent: :destroy

  accepts_nested_attributes_for :items, allow_destroy: true

  private
  def default_item_type
    self.item_type = @@ItemType if self.new_record?
  end
end

Subclassed Group model with ItemType set to another arbitrary model (in app/models/groups/gradation_group.rb):

class Groups::GradationGroup < Group
  @@ItemType = 'Gradation'
  has_many :items, through: :group_assignments, source: :groupable, source_type: @@ItemType, dependent: :destroy
end

My understanding is I had to change the namespace to something that is not a class name. I also had to change the group name to something other than what the items association will be composed of (in this case Gradation ).