Rails - Apr 2011 - AssociationTypeMismatch (<superclass> expected, got <subclass>)

Perhaps this is just
  http://www.ruby-forum.com/topic/1505406
coming back to bite me -- I suspect I''m missing a trivial declaration.

==== Error message (note that NOAA is an STI subclass of WeatherStation)

ActiveRecord::AssociationTypeMismatch (WeatherStation(#2169635200)
expected, got NOAA(#2185634180)):

==== Source of the error (station is, in fact, an NOAA object)

PremiseWeatherStation.create(:premise => self, :weather_station =>
station)

==== Models

class Premise < ActiveRecord::Base
  has_many :premise_weather_stations, :dependent => :destroy
  has_many :weather_stations, :through => :premise_weather_stations
  ...
end

class PremiseWeatherStation < ActiveRecord::Base
  belongs_to :premise
  belongs_to :weather_station
end

# WeatherStation is the ''parent'' of STI models
class WeatherStation < ActiveRecord::Base
  has_many :premise_weather_stations, :dependent => :destroy
  has_many :premises, :through => :premise_weather_stations
  ...
end

# NOAA is an STI subclass of WeatherStation
class NOAA < WeatherStation
  ...
end

==== Tables:

  create_table "premise_weather_stations", :force => true do |t|
    t.integer  "premise_id"
    t.integer  "weather_station_id"
    ...
  end

  create_table "premises", :force => true do |t|
    ...
  end

  create_table "weather_stations", :force => true do |t|
    t.string   "callsign"
    t.string   "type"    # for STI support
    ...
  end

===
I don''t think I''m doing anything "un-RAILs-ish". 
Any idea what I''m
missing?

- ff

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UPDATE:  Stranger and stranger.  I do NOT get this error running in the 
console.  I do NOT get this error running the test suite.  I ONLY get 
this error under ''rails server''.  I tracked the Rails source
to where
the AssociationTypeMismatch is raised in association_proxy.rb:

        def raise_on_type_mismatch(record)
          unless record.is_a?(@reflection.klass) || 
record.is_a?(@reflection.class_name.constantize)
            message = 
"#{@reflection.class_name}(##{@reflection.klass.object_id}) expected, 
got #{record.class}(##{record.class.object_id})"
            raise ActiveRecord::AssociationTypeMismatch, message
          end
        end

and inserted a Rails.logger.debug() statement.

When I''m running in the test suite, I see:

   >>> class=NOAA, record.is_a?(WeatherStation) => true, 
record.is_a?(WeatherStation) => true

When I''m running in under the server, the same run prints:

  >>> class=NOAA, record.is_a?(WeatherStation) => false, 
record.is_a?(WeatherStation) => false

Is there ANYTHING about the server environment (in development mode) 
that would account for is_a? behaving differently???

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On Fri, Apr 15, 2011 at 10:53 PM, Fearless Fool
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>wrote:
> Perhaps this is just
>  http://www.ruby-forum.com/topic/1505406
> coming back to bite me -- I suspect I''m missing a trivial
declaration.
>
> ==== Error message (note that NOAA is an STI subclass of WeatherStation)
>
> ActiveRecord::AssociationTypeMismatch (WeatherStation(#2169635200)
> expected, got NOAA(#2185634180)):
>
> ==== Source of the error (station is, in fact, an NOAA object)
>
> PremiseWeatherStation.create(:premise => self, :weather_station =>
> station)
>
>
I''ve been unable to reproduce your error in the rails server or in the
console. However, what I do see is that "self" is a reserved word. The
variable name of the object you want to pass in should not be called
"self".
When I used your statement as is I received a different TypeMismatch error;
it was for Premise because self was passing in PremiseWeatherStation. My
only suggestion right now is to change the variable name being passed into
:premise => to something else and try your statement again.

B.

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Hi Bryan:

Bryan Crossland wrote in post #993150:
>> PremiseWeatherStation.create(:premise => self, :weather_station
=>
>> station)
> I''ve been unable to reproduce your error in the rails server or in
the
> console. However, what I do see is that "self" is a reserved
word. The
> variable name of the object you want to pass in should not be called
> "self".
Thank you for digging around.  I should have shown more context --
''self'' is in fact what I intended:
========class Premise < ActiveRecord::Base
  has_many :premise_weather_stations, :dependent => :destroy
  has_many :weather_stations, :through => :premise_weather_stations
  ...
  def find_local_weather_stations
    stations = WeatherStation.find_stations_near(self)
    premise_weather_stations = stations.map do |station|
      PremiseWeatherStation.create(:premise => self, :weather_station =>
station)
    end
  end
  ...
end
========which is to say, find_local_weather_stations is an instance method which
associates this Premise (''self'') with a list of WeatherStation
(''station'') objects, creating a PremiseWeatherStation object
to form
each association.

What''s really odd is that I monkey patched the raise_on_type_mismatch()
method to print out the record and the @reflection.  Regardless of where
I run them (console, test, or server), they print out as the same.

HOWEVER, record.is_a?(@reflection.klass) returns true in the console or
test suite, false in the server.  I''m really mystified.

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On Sat, Apr 16, 2011 at 3:05 AM, Fearless Fool
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org> wrote:
> Hi Bryan:
>
> Bryan Crossland wrote in post #993150:
> >> PremiseWeatherStation.create(:premise => self, :weather_station
=>
> >> station)
> > I''ve been unable to reproduce your error in the rails server
or in the
> > console. However, what I do see is that "self" is a reserved
word. The
> > variable name of the object you want to pass in should not be called
> > "self".
>
> Thank you for digging around.  I should have shown more context --
> ''self'' is in fact what I intended:
> ========> class Premise < ActiveRecord::Base
>  has_many :premise_weather_stations, :dependent => :destroy
>  has_many :weather_stations, :through => :premise_weather_stations
>  ...
>   def find_local_weather_stations
>    stations = WeatherStation.find_stations_near(self)
>    premise_weather_stations = stations.map do |station|
>       PremiseWeatherStation.create(:premise => self, :weather_station
=>
> station)
>     end
>  end
>  ...
> end
> ========> which is to say, find_local_weather_stations is an instance
method which
> associates this Premise (''self'') with a list of
WeatherStation
> (''station'') objects, creating a PremiseWeatherStation
object to form
> each association.
>
> What''s really odd is that I monkey patched the
raise_on_type_mismatch()
> method to print out the record and the @reflection.  Regardless of where
> I run them (console, test, or server), they print out as the same.
>
> HOWEVER, record.is_a?(@reflection.klass) returns true in the console or
> test suite, false in the server.  I''m really mystified.
>
>
I don''t know why your monkey patch is showing one thing in the console
and
something else in the server. However I suspect that the reason is the same
as why you are getting the type mismatch in the first place. I believe it
has to do with how the find_stations_near method is working. Since I
don''t
know how you wrote that method I had to assume that what you were doing was
getting a list of WeatherStation objects. If I just grab all the
WeatherStation objects in my DB, regardless of if they are WeatherStation or
NOAA type and run them through your map and PremiseWeatherStation.create
statements they work fine. Both server and console. I ran it again but this
time told it to return all NOAA objects instead of WeatherStation. It worked
without issue. What is the code for the method find_stations_near?

B.

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Bryan Crossland wrote in post #993205:
> What is the code for the method find_stations_near?
First, here''s the code for find_local_weather_stations().  The create
method raises the error:

  def find_local_weather_stations(limit = 10)
    premise_weather_stations.delete_all
    stations = WeatherStation.find_stations_near(self)
    premise_weather_stations = stations[0, limit].map do |station|
      PremiseWeatherStation.create(:premise => self, :weather_station =>
station)
    end
  end

The find_stations_near(self) method calls an external web site to get
the callsigns, creates an in-memory "candidate" with that callsign,
and
then saves the candidate if not already in the database, or updates the
existing one if it is.  Both paths use the save!() method, so we can be
assured that the weather_station really is in the database.
find_stations_near() ultimately returns:

    def load_stations(stations)
      stations.map {|station| load_station(station) }
    end

    def load_station(candidate)
      if (incumbent WeatherStation.find_by_callsign(candidate.callsign))
        incumbent.resolve_location
        incumbent.save!
        incumbent
      else
        candidate.resolve_location
        candidate.save!
        candidate
      end
    end

I don''t see anything odd in that code.

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Okay, I have found a fix, or at least a workaround.  If a Rails core
team member is reading this, I''d appreciate knowing if this warrants a
lighthouse ticket.

If I add a .reload (to the AR that is already in the db):

def load_station(candidate)
      if (incumbent WeatherStation.find_by_callsign(candidate.callsign))
        incumbent.resolve_location
        incumbent.save!
        incumbent.reload      # RELOAD ADDED HERE
      else
        candidate.resolve_location
        candidate.save!
        candidate
      end
    end

... it no longer raises an AssociationTypeMismatch in this code (called
some lines later):

PremiseWeatherStation.create(:premise => self, :weather_station =>
station)

Mind you, this ONLY happens when run as a server and not in the console.
(See the OP for the schema and models).  I''m going back to work on
other
stuff, but if a Rails developer wants more information on this, I''d be
happy to provide it.

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