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bitterbal

2007-May-11 11:45 UTC

model methods when to use self

I am extending my model with some methods. My question is when to and
when not to define the method with self.

example

def sales_value
  ... all kinds of calculations
end

OR

def self.sales_value
  ... all kinds of calculations
end


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Yuri Leikind

2007-May-11 16:52 UTC

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Re: model methods when to use self

The shortest (but not the most correct one) way to describe the
difference is to say that def meth1; end is an object method while def
self.meth2; end is a class method, and you cal them differently:

a = Foo.new
a.meth1
Foo.meth2

But there''s more than that

As for Active Records it depends whether you want a method for an
ActiveRecord instance or for the class

Btw these are Ruby basics, find a good Ruby book/tutorial.

Cheers,
Yury

On 5/11/07, bitterbal <portie-kFg6fFbE636XDw4h08c5KA@public.gmane.org>
wrote:>
> I am extending my model with some methods. My question is when to and
> when not to define the method with self.
>
> example
>
> def sales_value
>   ... all kinds of calculations
> end
>
> OR
>
> def self.sales_value
>   ... all kinds of calculations
> end
>
>
> >
>

-- 
Best regards,
Yuri Leikind

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John Miller

2007-May-11 22:18 UTC

head link

Re: model methods when to use self

bitterbal wrote:> I am extending my model with some methods. My question is when to and
> when not to define the method with self.
> 
> example
> 
> def sales_value
>   ... all kinds of calculations
> end
> 
> OR
> 
> def self.sales_value
>   ... all kinds of calculations
> end
My answer is the same as Yuri''s, just different words.

If sales_value effects or returns a different value for each row in the 
table don''t use self.  You would then do this for example

sale = Sale.find(id)
puts "The sales value of sale #{id} is: #{sale}"

If sales_value combines data from some or all rows in the table use 
self.sales_value.  You might then do this:

sales = Sale.sales_value  #note there is no find here
puts "the value of all sales is #{sales}"

-- 
Posted via http://www.ruby-forum.com/.

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Robert Walker

2007-May-11 22:57 UTC

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Re: model methods when to use self

Maybe this will help you.

When you are writing model code you are writing a class.  That is
"working class" not "learnstitute class."

Think of "blue collar" and "white collar" workers.  People
of the
"blue collar" class work a certain way that is difference from a
"white collar" worker.  So you may have people (instances) of
"blue
collar" and "white" collar workers.

So you have a Class and some Objects of each class.  Both the Class
and the Objects can have methods (referred to as class and instance
methods respectively).

When you are writing your code you are writing a class represented in
the def as "self."

So.....

def self.my_class_method
  # Can be called on the Class or instances of the class
end

def my_instance_method
  # Is only available to instances of the class
end

Calling them.....

BlueCollarWorker.my_class_method       # called on the class
a_person_object.my_instance_method   #called on the instance.

On May 11, 6:18 pm, John Miller
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> bitterbal wrote:
> > I am extending my model with some methods. My question is when to and
> > when not to define the method with self.
>
> > example
>
> > def sales_value
> >   ... all kinds of calculations
> > end
>
> > OR
>
> > def self.sales_value
> >   ... all kinds of calculations
> > end
>
> My answer is the same as Yuri''s, just different words.
>
> If sales_value effects or returns a different value for each row in the
> table don''t use self.  You would then do this for example
>
> sale = Sale.find(id)
> puts "The sales value of sale #{id} is: #{sale}"
>
> If sales_value combines data from some or all rows in the table use
> self.sales_value.  You might then do this:
>
> sales = Sale.sales_value  #note there is no find here
> puts "the value of all sales is #{sales}"
>
> --
> Posted viahttp://www.ruby-forum.com/.

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Alain Ravet

2007-May-12 12:19 UTC

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Re: model methods when to use self

> I am extending my model with some methods. My question is when to  > and when not to define the method with self.


Ruby 101 :

    class String
      def shuffle
        split(//u).sort_by { rand }.join('''')
      end

      CHARS = ("a".."z").to_a +
("A".."Z").to_a + ("0".."9").to_a
      def self.random( len )
          newpass = ""
          1.upto(len) { |i| newpass << CHARS[rand(CHARS.size-1)] }
          return newpass
      end
    end

    puts String.random(10)
    puts "abcdef".shuffle



Alain Ravet
--------
http://blog.ravet.com/

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bitterbal

2007-May-13 06:39 UTC

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Re: model methods when to use self

Thanks. great example that makes it clear for me.

On May 12, 12:18 am, John Miller
<rails-mailing-l...-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:> bitterbal wrote:
> > I am extending my model with some methods. My question is when to and
> > when not to define the method with self.
>
> > example
>
> > def sales_value
> >   ... all kinds of calculations
> > end
>
> > OR
>
> > def self.sales_value
> >   ... all kinds of calculations
> > end
>
> My answer is the same as Yuri''s, just different words.
>
> If sales_value effects or returns a different value for each row in the
> table don''t use self.  You would then do this for example
>
> sale = Sale.find(id)
> puts "The sales value of sale #{id} is: #{sale}"
>
> If sales_value combines data from some or all rows in the table use
> self.sales_value.  You might then do this:
>
> sales = Sale.sales_value  #note there is no find here
> puts "the value of all sales is #{sales}"
>
> --
> Posted viahttp://www.ruby-forum.com/.

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Rails - May 2007 - model methods when to use self

model methods when to use self

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