Fixed bug not to restore association records

[kouyaf77]

Actually, we couldn't get association records at relation = self.send(name) of lib/mongoid/paranoia.rb.
In Rspec, subject had reference. But instance doesn't have reference when we use excepting Rspec.
So I fixed it.
Thx

[simi]

Hello @kouyaf77. Thanks for your pull request. Can you provide a little info why this change is needed? What's the usecase? Why you couldn't get association records via relation = self.send(name)?

[kouyaf77]

Hi @simi
There are some models the following.

class User
  include Mongoid::Document
  include Mongoid::Paranoia

  has_many :posts, dependent: :destroy
end

class Post
  include Mongoid::Document
  include Mongoid::Paranoia

  belongs_to :user
end

Then, we can't restore association records in case of following.
Because relation = self.send(name) is not got posts.

User.create posts: Post.create
user = User.first
user.destroy

user = User.unscoped.first
user.restore(recursive: true)

[kouyaf77]

The reason not to get association records is to work default scope.
So I fixed not to work default scope.

[johnnyshields]

@kouyaf77 Thank you for the PR and for fixing the tests. I'm a bit concerned about the change to Mongoid::Relations::Synchronization. This looks like it will leave in inverse references to paranoid documents which have been destroyed. I think it's better to remove the inverse references on paranoid destroy then recreate them after paranoid restore.

[johnnyshields]

Just looking at this again. Another option would be to move the deleted key to a shadow field (e.g. _deleted_user_id) and then restore the value later.

Again the main reason I don't like the solution in the PR is that it leaves you with a relation reference to a deleted object, which is a "messy" data state that doesn't (shouldn't) occur naturally in Mongoid.