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Object#is_a? is failing in the strangest way in Rails 3. I have single-table-inheritance set up as follows (simplified for brevity):

# resource.rb
class Resource < ActiveRecord::Base
  # blah blah
end

# video.rb
class Video < Resource
  # blah blah
end

In my controller, I have this:

def create
  @resource = Resource.find params[:resource_id]
  logger.info '@resource class: ' + @resource.class.name
  logger.info '@resource superclass: ' + @resource.class.superclass.name
  logger.info '@resource is_a?(Video): ' + @resource.is_a?(Video).inspect
  logger.info '@resource is_a?(Resource): ' + @resource.is_a?(Resource).inspect
  logger.info '@resource is_a?(ActiveRecord::Base): ' + @resource.is_a (ActiveRecord::Base).inspect
  # Do some other stuff
end

Invoking the #create action generates these log results:

@resource class: Video
@resource superclass: Resource
@resource is_a?(Video): true
@resource is_a?(Resource): false
@resource is_a?(ActiveRecord::Base): true

Note that the Video instance is an ActiveRecord::Base, yet it is not a Resource. This is not merely an academic concern. Framework code called from the action uses is_a? to check for a type mismatch, and it raises when it thinks the Video is not a Resource.

Yet in the Rails console, is_a?(Resource) returns true.

What in the world could be going on here?

rlkw1024
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2 Answers2

3

The solution is apparently to restart the Rails server process. I don't know how this error crept in, but it did. And what's more, it has happened on multiple occasions on multiple computers.

So, to anyone else experiencing this problem, just restart your server. Whatever it is, it's ephemeral.

rlkw1024
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  • I just stumbled onto this problem, and the comment fixed it. Is this issue reported as a bug? – pwnall Nov 22 '11 at 10:04
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    By the way, this happens because your parent model (Resource) is reloaded, but the model that inherits from it (Video) isn't. – pwnall Nov 22 '11 at 12:59
  • This comment did not help with rails 2.3.14 and ruby 1.8.7. – Sukima Apr 04 '12 at 19:35
0

Does the record you found have Video in its type column?

Searching on the superclass collection will find subclass objects, and I guess that even though you explicitly searched the Resource collection, the actual object you found was a Video.

No idea what the discrepancy is in the Rails console though! Rails overrides is_a? for ActiveSupport::TimeWithZone, but in your case Rails shouldn't be munging any class names or anything...

Maybe did you use different ids in the console and in your controller?

Andrew Grimm
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nfm
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  • Yes, it has Video in its type column. That's why it gets instantiated as a Video. But it seems to me that every Video should be a Resource--Rails or not, it's still Ruby inheritance. Video is a subclass of Resource, and is_a? looks at superclasses. And yes, I tried with the exact same IDs in the console and controller. – rlkw1024 Dec 07 '10 at 22:41
  • Also, I don't suppose it has anything to do with TimeWithZone, since that class's definition of is_a? wouldn't be used here. – rlkw1024 Dec 07 '10 at 22:46