Question

Code:

#schema..
  t.integer  "shares",             :default => 0
end

#model

def increment_shares
  shares = shares + 1 #undefined method + for nil class
  save
end

#console

  irb(main):003:0> t.shares
  => 0

  irb(main):004:0> t.shares = t.shares + 1
  => 1

  irb(main):005:0> t.increment_shares
  NoMethodError: undefined method `+' for nil:NilClass

(Problem should be clear from the code. Writing more text to meet ‘quality standards’)

Answer 1

You should use self to access a model’s attributes :

def increment_shares
  self.shares = self.shares + 1 
  self.save
end