Fix Mongoid dependent strategy

[fibrasek]

Again I ran againts some compability problems while using the gem with Mongoid. The first problem was the option dependent: :delete_all being passed to the model, which is wrong for Mongoid as stated in the documentation
The other is not quite a problem, just a minor refactoring, since the relation is being setup in the Impressionist::Impressionable module, there's no need to call Impressionist::SetupAssociation#set method.

As far as I tested in my application (locally and in production) there's no bigger problems in those changes.

Note: dependent: :delete does not triggers callbacks, I don't know if this can be a issue for some users.

[RickCarlino]

I know this is an old pull request, but it did fix some issues I was having on an application I work on.

Hopefully my comment will help anyone googling for a solution. I was only able to find unrelated fixes for a different gem and it took a while to isolate the cause.

The Problem

class FailingExample
  include Mongoid::Document

  is_impressionable counter_cache: true,
                    column_name: :impressions_field,
                    unique: :session_hash
  field :impressions_field, default: 0, type: Integer
end

FailingExample.create!

FailingExample.last.destroy # Crash!

# => NameError (uninitialized constant Mongoid::Relations::Cascading::DeleteAll)

The Solution

class FixedExample
  include Mongoid::Document

  is_impressionable counter_cache: true,
                    column_name: :impressions_field,
                    unique: :session_hash
  field :impressions_field, default: 0, type: Integer
  # ADD THIS LINE TO FIX ERROR (overrides dependent: :delete_all):
  has_many :impressions, as: :impressionable, dependent: :delete
end

FixedExample.create!

FixedExample.last.destroy # ok

Notes

I am using Mongoid v6.

[fibrasek]

Is this problem already solved? If not is it still relevant?