Rails - Sep 2009 - how to compare two model instances? is "m1.to_yaml.eql?(m2.to_yaml)" a good way?

Hi,

What''s an easy way to compare for equality two model instances (that
haven''t been saved yet).  Or in other words pretty much just two
object instances.  I''ve tried "==" and "eql?" on
the objects directly
and this doesn''t work.

How about:  "m1.to_yaml.eql?(m2.to_yaml)"      Is this the simplest
way?

-- 
Greg
http://blog.gregnet.org/

On Sep 5, 9:30 am, Greg Hauptmann
<greg.hauptmann.r...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi,
>
> What''s an easy way to compare for equality two model instances
(that
> haven''t been saved yet).  Or in other words pretty much just two
> object instances.  I''ve tried "==" and "eql?"
on the objects directly
> and this doesn''t work.
>
> How about:  "m1.to_yaml.eql?(m2.to_yaml)"      Is this the
simplest way?
Compare their attributes ?

Fred
>
> --
> Greghttp://blog.gregnet.org/

2009/9/5 Frederick Cheung
<frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
> Compare their attributes ?
>
> Fred
Guess I was looking for an automated way to do this if one existed?
or is there some concept of having to implement some basic comparison
class in Ruby & then being able to have the "==" method work?

tks

On Sep 5, 12:09 pm, Greg Hauptmann
<greg.hauptmann.r...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> 2009/9/5 Frederick Cheung
<frederick.che...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
>
> > Compare their attributes ?
>
> > Fred
>
> Guess I was looking for an automated way to do this if one existed?
> or is there some concept of having to implement some basic comparison
> class in Ruby & then being able to have the "==" method work?
>
Classes can implement their own == method. ActiveRecord::Base does do
this, just not the way you want it too - ActiveRecord considers two
objects to be equal if they correspond to the same row in the database
(ie have the same id). If you have two unsaved objects then saving
them would yield two different rows in the database, therefore by AR''s
reckoning they are not equal. While you could override == on your
class that may well break bits of ActiveRecord that expects == to
behave in a certain way.

Fred

2009/9/6 Frederick Cheung
<frederick.cheung-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>:
> Classes can implement their own == method. ActiveRecord::Base does do
> this, just not the way you want it too - ActiveRecord considers two
> objects to be equal if they correspond to the same row in the database
> (ie have the same id). If you have two unsaved objects then saving
> them would yield two different rows in the database, therefore by
AR''s
> reckoning they are not equal. While you could override == on your
> class that may well break bits of ActiveRecord that expects == to
> behave in a certain way.
thanks for the advice Frederick - I think I''ll just implement my own
"custom_eql?" method on my class then to be safe....