Rails - Aug 2006 - Hard time understanding the differences between "def self.foo" and "def foo"

Hi guys,

I''m having a little trouble understanding the differences and knowing  
when to use "def foo" and "def self.foo" in my models.  I
don''t quite
understand them and was hoping someone could explain or give me  
examples on how to use the "self." properly.

For example, I had "def foo" in my model "Account" and in
one of my
views I tried doing "<%= Account.foo %>" but it didn''t
work, but when
I changed it to "def self.foo" it did.  But I don''t know why.

Thanks for the help.

Hey Rob,

The difference is between a Class and an Object. (btw, this is basic  
object oriented stuff you''ll find in any reference)

Examples work best;

Dog is a Class, and your dog Fido is an Object (a specific instance  
of a Dog).

So Dog.new references the Class method new, which gives you a new dog.

fido = Dog.new

and on fido, you can do specific dog things.

dog.sniff!
dog.eat(food)

etc.

in terms of ruby, you define a Class method as:
def self.new
end

and a object (aka instance) method
def sniff!
end

hope that helps Rob.
(I tried to work in some ''mongrel'' references, but that
started to
look like a subclass of dog that complicated the matter)

cheers,
Jodi

On 14-Aug-06, at 11:24 PM, Rob Gabaree wrote:
> Hi guys,
>
> I''m having a little trouble understanding the differences and  
> knowing when to use "def foo" and "def self.foo" in my
models.  I
> don''t quite understand them and was hoping someone could explain
or
> give me examples on how to use the "self." properly.
>
> For example, I had "def foo" in my model "Account" and
in one of my
> views I tried doing "<%= Account.foo %>" but it
didn''t work, but
> when I changed it to "def self.foo" it did.  But I don''t
know why.
>
> Thanks for the help.
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Hi Jodi,

Thanks.  So can you tell me if I understand this correctly?

Instance methods are defined without the "self." and are accessible  
to all new class instances (objects)?

Class methods are defined with the "self." and can be accessed by  
themselves using Class.method? and dont require a new class instance?

So like..

class Dog

def self.find_owner (id)
self.find_by_owner(id)
end

def set_new_owner(owner)
self.owner = owner
end

end

so if i just wanted to find a random persons owner, i can just do...

owner = Dog.find_owner(1)
owner = Dog.find_owner(5)

without creating any new objects / class instances.. and if I want to  
create a new dog and give it a new owner''s name i can do..

fido = Dog.new(:name => "fido", :owner => "rob")
fido.set_new_owner="jerry"
fido.save

Am I on the right track?


On Aug 14, 2006, at 11:34 PM, Jodi Showers wrote:
> Hey Rob,
>
> The difference is between a Class and an Object. (btw, this is  
> basic object oriented stuff you''ll find in any reference)
>
> Examples work best;
>
> Dog is a Class, and your dog Fido is an Object (a specific instance  
> of a Dog).
>
> So Dog.new references the Class method new, which gives you a new dog.
>
> fido = Dog.new
>
> and on fido, you can do specific dog things.
>
> dog.sniff!
> dog.eat(food)
>
> etc.
>
> in terms of ruby, you define a Class method as:
> def self.new
> end
>
> and a object (aka instance) method
> def sniff!
> end
>
> hope that helps Rob.
> (I tried to work in some ''mongrel'' references, but that
started to
> look like a subclass of dog that complicated the matter)
>
> cheers,
> Jodi
>
> On 14-Aug-06, at 11:24 PM, Rob Gabaree wrote:
>
>> Hi guys,
>>
>> I''m having a little trouble understanding the differences and
>> knowing when to use "def foo" and "def self.foo" in
my models.  I
>> don''t quite understand them and was hoping someone could
explain
>> or give me examples on how to use the "self." properly.
>>
>> For example, I had "def foo" in my model "Account"
and in one of
>> my views I tried doing "<%= Account.foo %>" but it
didn''t work,
>> but when I changed it to "def self.foo" it did.  But I
don''t know
>> why.
>>
>> Thanks for the help.
>> _______________________________________________
>> Rails mailing list
>> Rails@lists.rubyonrails.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Well, almost.
find_owner would be calling find_by_owner on the Dog class.
So, it would return an array of Dog objects, not owner(s).

Your set_new_owner(owner) method is right, but there''s a better way.
fido.owner = "jerry"
fido.save

If you need to override the default accessor, you can do that:
def owner=(new_name)
  self.name = new_name.capitalize # always store names capitalized
end

Make sense?

  -- Wes

On 8/15/06, Rob Gabaree <lists@rawb.net> wrote:
>
> Hi Jodi,
>
> Thanks.  So can you tell me if I understand this correctly?
>
> Instance methods are defined without the "self." and are
accessible
> to all new class instances (objects)?
>
> Class methods are defined with the "self." and can be accessed by
> themselves using Class.method? and dont require a new class instance?
>
> So like..
>
> class Dog
>
> def self.find_owner (id)
> self.find_by_owner(id)
> end
>
> def set_new_owner(owner)
> self.owner = owner
> end
>
> end
>
> so if i just wanted to find a random persons owner, i can just do...
>
> owner = Dog.find_owner(1)
> owner = Dog.find_owner(5)
>
> without creating any new objects / class instances.. and if I want to
> create a new dog and give it a new owner''s name i can do..
>
> fido = Dog.new(:name => "fido", :owner => "rob")
> fido.set_new_owner="jerry"
> fido.save
>
> Am I on the right track?
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Rob -

The find_by_owner Class method Wes mentions is provided to you by  
Rails - as well as a bunch of others per finders field (find_by_# 
{field_name})

Plus rails gives you accessors (instance methods) for every column in  
your database. So fido.owner (fido.size, fido. color) will be  
automatically available with the following class definition:

class Dog < ActiveRecord::Base
end

you get a bunch of free instance and class methods - as long as you  
follow the rails naming conventions (tablename is ''dog'', and
has a
column id : integer [primary key]).

Rob - I suggest you pickup one of the great rails tutorials. You''ll  
get a more complete picture than we can provide - http:// 
www.pragmaticprogrammer.com/title/rails1/ is a definitely worthwhile.

Jodi

On 15-Aug-06, at 11:53 AM, Wes Garrison wrote:
> Well, almost.
> find_owner would be calling find_by_owner on the Dog class.
> So, it would return an array of Dog objects, not owner(s).
>
> Your set_new_owner(owner) method is right, but there''s a better
way.
> fido.owner = "jerry"
> fido.save
>
> If you need to override the default accessor, you can do that:
> def owner=(new_name)
>   self.name = new_name.capitalize # always store names capitalized
> end
>
> Make sense?
>
>   -- Wes
>
> On 8/15/06, Rob Gabaree <lists@rawb.net> wrote:
> Hi Jodi,
>
> Thanks.  So can you tell me if I understand this correctly?
>
> Instance methods are defined without the "self." and are
accessible
> to all new class instances (objects)?
>
> Class methods are defined with the "self." and can be accessed by
> themselves using Class.method? and dont require a new class instance?
>
> So like..
>
> class Dog
>
> def self.find_owner (id)
> self.find_by_owner(id)
> end
>
> def set_new_owner(owner)
> self.owner = owner
> end
>
> end
>
> so if i just wanted to find a random persons owner, i can just do...
>
> owner = Dog.find_owner(1)
> owner = Dog.find_owner(5)
>
> without creating any new objects / class instances.. and if I want to
> create a new dog and give it a new owner''s name i can do..
>
> fido = Dog.new(:name => "fido", :owner => "rob")
> fido.set_new_owner="jerry"
> fido.save
>
> Am I on the right track?
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails
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Thanks.  I already knew that you can use find_by_fieldname with rails  
as well as getting field names automatically with fido.name,  
fido.owner, etc.. I just used those as examples to see if I  
understood the difference between instance methods and class methods....

On Aug 15, 2006, at 12:34 PM, Jodi Showers wrote:
> Rob -
>
> The find_by_owner Class method Wes mentions is provided to you by  
> Rails - as well as a bunch of others per finders field (find_by_# 
> {field_name})
>
> Plus rails gives you accessors (instance methods) for every column  
> in your database. So fido.owner (fido.size, fido. color) will be  
> automatically available with the following class definition:
>
> class Dog < ActiveRecord::Base
> end
>
> you get a bunch of free instance and class methods - as long as you  
> follow the rails naming conventions (tablename is ''dog'',
and has a
> column id : integer [primary key]).
>
> Rob - I suggest you pickup one of the great rails tutorials.
You''ll
> get a more complete picture than we can provide - http:// 
> www.pragmaticprogrammer.com/title/rails1/ is a definitely worthwhile.
>
> Jodi
>
> On 15-Aug-06, at 11:53 AM, Wes Garrison wrote:
>
>> Well, almost.
>> find_owner would be calling find_by_owner on the Dog class.
>> So, it would return an array of Dog objects, not owner(s).
>>
>> Your set_new_owner(owner) method is right, but there''s a
better way.
>> fido.owner = "jerry"
>> fido.save
>>
>> If you need to override the default accessor, you can do that:
>> def owner=(new_name)
>>   self.name = new_name.capitalize # always store names capitalized
>> end
>>
>> Make sense?
>>
>>   -- Wes
>>
>> On 8/15/06, Rob Gabaree <lists@rawb.net> wrote: Hi Jodi,
>>
>> Thanks.  So can you tell me if I understand this correctly?
>>
>> Instance methods are defined without the "self." and are
accessible
>> to all new class instances (objects)?
>>
>> Class methods are defined with the "self." and can be
accessed by
>> themselves using Class.method? and dont require a new class instance?
>>
>> So like..
>>
>> class Dog
>>
>> def self.find_owner (id)
>> self.find_by_owner(id)
>> end
>>
>> def set_new_owner(owner)
>> self.owner = owner
>> end
>>
>> end
>>
>> so if i just wanted to find a random persons owner, i can just do...
>>
>> owner = Dog.find_owner(1)
>> owner = Dog.find_owner(5)
>>
>> without creating any new objects / class instances.. and if I want to
>> create a new dog and give it a new owner''s name i can do..
>>
>> fido = Dog.new(:name => "fido", :owner =>
"rob")
>> fido.set_new_owner="jerry"
>> fido.save
>>
>> Am I on the right track?
>>
>> _______________________________________________
>> Rails mailing list
>> Rails@lists.rubyonrails.org
>> http://lists.rubyonrails.org/mailman/listinfo/rails
>
> _______________________________________________
> Rails mailing list
> Rails@lists.rubyonrails.org
> http://lists.rubyonrails.org/mailman/listinfo/rails