Issues with Ruby's defined? operator in Rails

Question

I have an instance method on my Writer class that uses the defined? operator to check and see if posted_posts is defined:

def performance_score
  logger.debug posted_posts
  logger.debug defined?(posted_posts)
  unless defined?(posted_posts)
    ...
  else
    ...
  end
end

In my controller I have a writers instance defined as follows:

@writers = Writer.select("writers.*, p.total_posts, p.posted_posts").joins(...)

When I call @writers.performance_score, from the first logger.debug line it says I have 4 posted_posts, but the second prints out nil. Furthermore, it goes into the unless section instead of the else.

To test this, I stub out the posted_posts to 4. This prints out 4 from the first logger.debug line and the second logger.debug says it is defined as a method. Furthermore, it does go into the else.

Can you please help me understand why this is failing in my Rails application?

Answer 1

It is likely failing in reality because the relation returned from your AREL select statement uses method_missing magic to return a value from the call. This is not the same thing as being defined. When you mock/stub the "method" on your test object it is likely using the define_method function which is creating a defined function.

This may do what you want instead.

if respond_to?(:posted_posts)
  ...
else
  ...
end