Rails - Aug 2008 - how to apply a class method to a limited collection of the objects?

Hi,
I just can''t figure out how to do it, i''m sure it''s
pretty simple: I
have a model Order with a few named_scope methods
(:completed, :incompleted, :recent). Now I''d like to define a method
that returns the latest date an order was placed. The method shouldn''t
just do this over the entire collection of orders, but also over any
of the scopes. I know how to define a method within a specific scope
(named_scope :recent do def latest_date <...> end end), but surely
there''s a way I don''t need to define it 3 times to be able to
access
it within each scope?

If I define the class method Order#latest_date, how can I call it on a
subset of orders, either found by a named_scope or any other
find(:conditions => ...) method?

Dirk.
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I think you are mixing up class and instance methods, maybe im wrong
but:

If every order in the system has a latest_date, or every order has a
way of finding it out, your method should be a instance method. so

class Order < AR::Base
   named_scope :recent
   named_scope :whatever

   def latest_date
      self.order_date - Time.now # or however you compute it
   end
end


when you get an order may it be via a find or a named scope (which is
just a find with some constraints), you can always call the method on
the instance.

A class method would work if all orders had the same latest_date,
which i cant figure out why would that be.

am i close?  i might be mumblinng crap.

let me know
On Aug 21, 10:28 am, deegee
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi,
> I just can''t figure out how to do it, i''m sure
it''s pretty simple: I
> have a model Order with a few named_scope methods
> (:completed, :incompleted, :recent). Now I''d like to define a
method
> that returns the latest date an order was placed. The method
shouldn''t
> just do this over the entire collection of orders, but also over any
> of the scopes. I know how to define a method within a specific scope
> (named_scope :recent do def latest_date <...> end end), but surely
> there''s a way I don''t need to define it 3 times to be
able to access
> it within each scope?
>
> If I define the class method Order#latest_date, how can I call it on a
> subset of orders, either found by a named_scope or any other
> find(:conditions => ...) method?
>
> Dirk.
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Ok, I think I didn''t make myself clear on that one. No I know the
difference
between class and instance methods. My Orders have a date attribute.
I''m
looking to find the most recent order based on that date attribute. If I
want to do that on *all* Orders, I can just define a class method:

class Order < AR::Base
  named_scope :whatever, :conditions => ...

  def self.latest_date
    latest_order = first(:order => ''date DESC'')
    latest_order.date
  end

end

I can then do Order.latest_date to get the date of the most recent order.
But I can''t do Order.whatever.latest_date to find the latest order
within
the group of ''whatever'' orders. That''s what
I''m trying to do. Of course, in
the simple case above, I could just do

Order.whatever.first(:order => ''date DESC'').date

and because it''s quite a simple query, that''s okay, but for
more complex
calculations based on a collection of objects, that would not be very DRY.

Can''t use instance method here because a specific Order object
doesn''t have
the knowlegde about latest_date.

Dirk.



On Thu, Aug 21, 2008 at 12:04 PM, Wolas!
<jcpenche-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> I think you are mixing up class and instance methods, maybe im wrong
> but:
>
> If every order in the system has a latest_date, or every order has a
> way of finding it out, your method should be a instance method. so
>
> class Order < AR::Base
>   named_scope :recent
>   named_scope :whatever
>
>   def latest_date
>      self.order_date - Time.now # or however you compute it
>   end
> end
>
>
> when you get an order may it be via a find or a named scope (which is
> just a find with some constraints), you can always call the method on
> the instance.
>
> A class method would work if all orders had the same latest_date,
> which i cant figure out why would that be.
>
> am i close?  i might be mumblinng crap.
>
> let me know
> On Aug 21, 10:28 am, deegee
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > Hi,
> > I just can''t figure out how to do it, i''m sure
it''s pretty simple: I
> > have a model Order with a few named_scope methods
> > (:completed, :incompleted, :recent). Now I''d like to define a
method
> > that returns the latest date an order was placed. The method
shouldn''t
> > just do this over the entire collection of orders, but also over any
> > of the scopes. I know how to define a method within a specific scope
> > (named_scope :recent do def latest_date <...> end end), but
surely
> > there''s a way I don''t need to define it 3 times to
be able to access
> > it within each scope?
> >
> > If I define the class method Order#latest_date, how can I call it on a
> > subset of orders, either found by a named_scope or any other
> > find(:conditions => ...) method?
> >
> > Dirk.
> >
>
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Maybe I found an answer to my own question. I already knew I could
define an extension on a named_scope:
named_scope :whatever, :conditions => ... do
   def latest_date
       first(:order => ''date DESC'').date
   end
end
As I stated in my first post, I need to define the same extension for
all my scopes.

It looks like I can use the :extend options, like on associations, to
put my extension in a Module and re-use in all my scopes:
named_scope :whatever, :conditions => ..., :extend => FindLatestDate

Module FindLatestDate
  def latest_date
    first(:order => ''date DESC'').date
  end
end

I''ll try this and let you know if it works. Actually, the book AWDWR
has so much information, it''s just a matter of reading 3-4 times to
grasp the gritty details...

On 21 aug, 16:56, "Dirk Groten"
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Ok, I think I didn''t make myself clear on that one. No I know the
difference
> between class and instance methods. My Orders have a date attribute.
I''m
> looking to find the most recent order based on that date attribute. If I
> want to do that on *all* Orders, I can just define a class method:
>
> class Order < AR::Base
>   named_scope :whatever, :conditions => ...
>
>   def self.latest_date
>     latest_order = first(:order => ''date DESC'')
>     latest_order.date
>   end
>
> end
>
> I can then do Order.latest_date to get the date of the most recent order.
> But I can''t do Order.whatever.latest_date to find the latest order
within
> the group of ''whatever'' orders. That''s what
I''m trying to do. Of course, in
> the simple case above, I could just do
>
> Order.whatever.first(:order => ''date DESC'').date
>
> and because it''s quite a simple query, that''s okay, but
for more complex
> calculations based on a collection of objects, that would not be very DRY.
>
> Can''t use instance method here because a specific Order object
doesn''t have
> the knowlegde about latest_date.
>
> Dirk.
>
> On Thu, Aug 21, 2008 at 12:04 PM, Wolas!
<jcpen...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > I think you are mixing up class and instance methods, maybe im wrong
> > but:
>
> > If every order in the system has a latest_date, or every order has a
> > way of finding it out, your method should be a instance method. so
>
> > class Order < AR::Base
> >   named_scope :recent
> >   named_scope :whatever
>
> >   def latest_date
> >      self.order_date - Time.now # or however you compute it
> >   end
> > end
>
> > when you get an order may it be via a find or a named scope (which is
> > just a find with some constraints), you can always call the method on
> > the instance.
>
> > A class method would work if all orders had the same latest_date,
> > which i cant figure out why would that be.
>
> > am i close?  i might be mumblinng crap.
>
> > let me know
> > On Aug 21, 10:28 am, deegee
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > Hi,
> > > I just can''t figure out how to do it, i''m sure
it''s pretty simple: I
> > > have a model Order with a few named_scope methods
> > > (:completed, :incompleted, :recent). Now I''d like to
define a method
> > > that returns the latest date an order was placed. The method
shouldn''t
> > > just do this over the entire collection of orders, but also over
any
> > > of the scopes. I know how to define a method within a specific
scope
> > > (named_scope :recent do def latest_date <...> end end), but
surely
> > > there''s a way I don''t need to define it 3 times
to be able to access
> > > it within each scope?
>
> > > If I define the class method Order#latest_date, how can I call it
on a
> > > subset of orders, either found by a named_scope or any other
> > > find(:conditions => ...) method?
>
> > > Dirk.
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Please let me know how it works out.


On Aug 21, 4:43 pm, deegee
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Maybe I found an answer to my own question. I already knew I could
> define an extension on a named_scope:
> named_scope :whatever, :conditions => ... do
>    def latest_date
>        first(:order => ''date DESC'').date
>    end
> end
> As I stated in my first post, I need to define the same extension for
> all my scopes.
>
> It looks like I can use the :extend options, like on associations, to
> put my extension in a Module and re-use in all my scopes:
> named_scope :whatever, :conditions => ..., :extend => FindLatestDate
>
> Module FindLatestDate
>   def latest_date
>     first(:order => ''date DESC'').date
>   end
> end
>
> I''ll try this and let you know if it works. Actually, the book
AWDWR
> has so much information, it''s just a matter of reading 3-4 times
to
> grasp the gritty details...
>
> On 21 aug, 16:56, "Dirk Groten"
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
> > Ok, I think I didn''t make myself clear on that one. No I know
the difference
> > between class and instance methods. My Orders have a date attribute.
I''m
> > looking to find the most recent order based on that date attribute. If
I
> > want to do that on *all* Orders, I can just define a class method:
>
> > class Order < AR::Base
> >   named_scope :whatever, :conditions => ...
>
> >   def self.latest_date
> >     latest_order = first(:order => ''date DESC'')
> >     latest_order.date
> >   end
>
> > end
>
> > I can then do Order.latest_date to get the date of the most recent
order.
> > But I can''t do Order.whatever.latest_date to find the latest
order within
> > the group of ''whatever'' orders. That''s what
I''m trying to do. Of course, in
> > the simple case above, I could just do
>
> > Order.whatever.first(:order => ''date DESC'').date
>
> > and because it''s quite a simple query, that''s okay,
but for more complex
> > calculations based on a collection of objects, that would not be very
DRY.
>
> > Can''t use instance method here because a specific Order
object doesn''t have
> > the knowlegde about latest_date.
>
> > Dirk.
>
> > On Thu, Aug 21, 2008 at 12:04 PM, Wolas!
<jcpen...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > > I think you are mixing up class and instance methods, maybe im
wrong
> > > but:
>
> > > If every order in the system has a latest_date, or every order
has a
> > > way of finding it out, your method should be a instance method.
so
>
> > > class Order < AR::Base
> > >   named_scope :recent
> > >   named_scope :whatever
>
> > >   def latest_date
> > >      self.order_date - Time.now # or however you compute it
> > >   end
> > > end
>
> > > when you get an order may it be via a find or a named scope
(which is
> > > just a find with some constraints), you can always call the
method on
> > > the instance.
>
> > > A class method would work if all orders had the same latest_date,
> > > which i cant figure out why would that be.
>
> > > am i close?  i might be mumblinng crap.
>
> > > let me know
> > > On Aug 21, 10:28 am, deegee
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > > > Hi,
> > > > I just can''t figure out how to do it, i''m
sure it''s pretty simple: I
> > > > have a model Order with a few named_scope methods
> > > > (:completed, :incompleted, :recent). Now I''d like
to define a method
> > > > that returns the latest date an order was placed. The method
shouldn''t
> > > > just do this over the entire collection of orders, but also
over any
> > > > of the scopes. I know how to define a method within a
specific scope
> > > > (named_scope :recent do def latest_date <...> end
end), but surely
> > > > there''s a way I don''t need to define it 3
times to be able to access
> > > > it within each scope?
>
> > > > If I define the class method Order#latest_date, how can I
call it on a
> > > > subset of orders, either found by a named_scope or any other
> > > > find(:conditions => ...) method?
>
> > > > Dirk.- Hide quoted text -
>
> - Show quoted text -
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Yes, tried it out and it works perfectly. I looks like all the options
you can use for associations can also be used on scopes, which is
really cool!

On 21 aug, 18:48, "\"Wolas!\""
<jcpen...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Please let me know how it works out.
>
> On Aug 21, 4:43 pm, deegee
<dirkgro...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > Maybe I found an answer to my own question. I already knew I could
> > define an extension on a named_scope:
> > named_scope :whatever, :conditions => ... do
> >    def latest_date
> >        first(:order => ''date DESC'').date
> >    end
> > end
> > As I stated in my first post, I need to define the same extension for
> > all my scopes.
>
> > It looks like I can use the :extend options, like on associations, to
> > put my extension in a Module and re-use in all my scopes:
> > named_scope :whatever, :conditions => ..., :extend =>
FindLatestDate
>
> > Module FindLatestDate
> >   def latest_date
> >     first(:order => ''date DESC'').date
> >   end
> > end
>
> > I''ll try this and let you know if it works. Actually, the
book AWDWR
> > has so much information, it''s just a matter of reading 3-4
times to
> > grasp the gritty details...
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