model methods when to use self

rubyonrails-talk
1

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

2

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

3

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.

4

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

5

Thanks. great example that makes it clear for me.