Rails: replacing try with the Null Object Pattern

Question

In most of my applications, I have a `current_user` method. To avoid exceptions in cases like `current_user.name` where `current_user` is `nil`, rails provides the `try` method. The problem with this is that I need to remember to use `try` wherever `current_user` might be `nil`. I want to use the Null Object pattern to remove this additional overhead. ``` class NullUser def method_missing(method_name, *args) nil end end def current_user return NullUser.new unless UserSession.find @current_user ||= UserSession.find.user end ``` This can replace `try` in some cases: ``` current_user.try(:first_name) #=> nil current_user.first_name #=> nil ``` but fails with further chaining: ``` current_user.profiles.first.name #=> undefined method... ``` I tried to return the null object: ``` class NullUser def method_missing(method_name, *args) self.class.new end end current_user.try { |u| u.profiles.first.name } #=> nil current_user.profiles.first.name #=> nil ``` but this would fail in other cases:…

Accepted Answer

I would stick with the `NullUser` but change its name to `GuestUser` to make things clearer. Additionally you should stub all important method from your User class, e.g.

```
class GuestUser
  def method_missing(method_name, *args)
    nil
  end

def is_admin?
    false
  end

# maybe even fields:
  def name
    "Guest"
  end

# ...
end
```

Rails: replacing try with the Null Object Pattern

Solution

Problem