I'm experiencing some weirdness that didn't seem to be the case in ActiveRecord. Note that I'm working with a legacy database so I need to assign the foreign key on the `users` collection.

```
class User
include Mongoid::Document
include Mongoid::Timestamps

belongs_to :company, foreign_key: "companyId"
end

class Company
include Mongoid::Document
include Mongoid::Timestamps

has_many :users
end
```
Ok that all looks good to me. But when I do the following on the console, a `Company` is created, but the `User` isn't saved with the `companyId` set on it.

```
user.create_company(name: "My cool company")
```

Instead I have to add a `#save` call on `user` like so...

```
user.create_company(name: "My cool company")
user.save
```

Shouldn't `create_company` save the `User` record?