How come this works and doesn't work in IRB?

I have Users . Users have_many :organizations

If I do:

User.find(:all).select {|u| u.organizations.first.name 开发者_如何学运维}

it returns with:

NoMethodError: You have a nil object when you didn't expect it!
The error occurred while evaluating nil.name
from (irb):33
from (irb):33:in `select'
from (irb):33

Long story short:

I am trying to find the names of the first organization from each user.

---

Because one of your users does not have any organizations so organizations.first is nil

You can prevent this by doing

User.find(:all).select {|u| 
  u.organizations.first.name unless u.organizations.size == 0}