Simplify multiple nil checking in Rails

Question

How should I write:

if @parent.child.grand_child.attribute.present?
  do_something

without cumbersome nil checkings to avoid exception:

Answer 1

I suppose you can do it using a delegate method as a result you'll have sth like

@parent.child_grand_child_attribute.present?

Answer 2

Rails has object.try(:method):

if @parent.try(:child).try(:grand_child).try(:attribute).present?
   do_something

http://api.rubyonrails.org/classes/Object.html#method-i-try

Answer 3

All these answers are old, so I thought I should share more modern options.

If you are getting an association that might not exist:

@parent&.child&.grand_child&.attribute

if you are reaching into a hash for a key that might not exist:

hash = {
 parent_key: {
   some_other_key: 'a value of some sort'
 },
 different_parent_key: {
   child_key: {
     grand_child: {
       attribute: 'thing'
     }
   }
 }
}
hash.dig(:parent_key, :child_key, :grandchild_key)

Either of these will gracefully return nil if child, grandchild, or attribute don't exist

Answer 4

For fun, you could use a fold:

[:child, :grandchild, :attribute].reduce(@parent){|mem,x| mem = mem.nil? ? mem : mem.send(x) } 

but using andand is probably better, or ick, which I like a lot and has methods like try and maybe.

Answer 5

You can slightly reduce it by assigning the intermediate values to some local variable:

if a = @parent.child and a = a.grandchild and a.attribute

Answer 6

You coult just catch the exception:

begin
  do something with parent.child.grand_child.attribute
rescue NoMethodError => e
  do something else
end