`attributes` returns a `Hash` or a `Bson::Document` depending on what method was used to fetch the object. It's a hash after `create` and `reload`, but a `Bson::Document` after find. This means that attributes can't be consistently accessed with symbols as keys.

```ruby

class Test

  include Mongoid::Document

end

> t = Test.create

=> #<Test _id: 627a49ef69ca9cc6b8bacb59, >

> t.attributes.class

=> Hash

> t1 = Test.find('627a49ef69ca9cc6b8bacb59')

=> #<Test _id: 627a49ef69ca9cc6b8bacb59, >

> t1.attributes.class

=> BSON::Document

> t1.attributes[:_id]

=> BSON::ObjectId('627a49ef69ca9cc6b8bacb59')

> t1.reload.attributes.class

=> Hash

> t1.reload.attributes[:_id]

=> nil

```