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

If the attribute you are checking is always the same, create a method in @parent.

def attribute_present?
  @parent.child.present? && @parent.child.grandchild.present? && @parent.child.grandchild.attribute.present?

end

Alternatively, create has_many :through relationship so that @parent can get to grandchild so that you can use :

@parent.grandchild.try(:attribute).try(:present?)

Note: present? is not just for nil, it also checks for blank values, ''. You can just do @parent.grandchild.attribute if it's just nil checking

Answer 2

Hi Think you can use a flag variable here with rescue option

flag = @parent.child.grand_child.attribute.present? rescue false

if flag
do_something
end

Answer 3

You could do this:

Optional = Struct.new(:value) do
  def and_then(&block)
    if value.nil?
      Optional.new(nil)
    else
      block.call(value)
    end
  end

  def method_missing(*args, &block)
    and_then do |value|
      Optional.new(value.public_send(*args, &block))
    end
  end
end

Your check would become:

if Optional.new(@parent).child.grand_child.attribute.present?
  do_something

Source: http://codon.com/refactoring-ruby-with-monads

Answer 4

You could use Object#andand.

With it your code would look like this:

if @parent.andand.child.andand.grandchild.andand.attribute