Why can't I access attributes in rails model?

Rails
1

Hi, I’d like to know why I can’t, or how can I, access attributes like
that:

class User < ActiveRecord::Base
def name
@first_name + @last_name
end
end

first_name and last_name are user attributes in the database.

Thanks in advance.

2

Have this instance variables been set anywhere in your app?

If not, you wont be able to access attributes anywhere.

I suggest to first find a record in the DB and set the results to and
instance variable like:

@var = User.find(params[:some_params])

and then you will be able to access attributes for that object

@var.name + @var.lastname

2012/1/30 Rodrigo R. [email protected]

3

On Mon, Jan 30, 2012 at 9:09 PM, Rodrigo R.
[email protected]wrote:

ActiveRecord dynamically defines “accessor methods” on the
user instance.

That user instance is accessible as ‘self’ inside the user instance,
so you could do

class User < ActiveRecord::Base
def name
self.first_name + self.last_name
end
end

But, in Ruby, when using a read accessor, you could also write it
without the explicit ‘self’.

class User < ActiveRecord::Base
def name
first_name + last_name

same as self.first_name + self.last_name

if there is no first_name, last_name local variable

defined in the scope

end
end

For write accessors, you must put the self in front, that is:

self.full_name = “#{first_name} #{last_name}”

And the @first_name you asked about, that is an “instance variable”.

Read one of the many Ruby tutorials or books to understand this better.

HTH,

Peter

4

On Mon, Jan 30, 2012 at 9:59 PM, Rodrigo R.
[email protected]wrote:

Thank you, but I knew that, I did that (use self to do what I want) before
I asked the question.

I’d just like to know why can’t I use @first_name instead of
self.first_name, to me it seems like the same thing inside the model.

They are not:

@first_name is an “instance variable”. You could set it like this:

@first_name = user.first_name

but it is not automatically set, and it is also not typically used like
that.

A more typical use would be:

@user = User.find(params[:id])

and then you can use @user in the controller, but also in the views,
due to the set-up of Rails.

self.first_name is a method that is dynamically provided by
ActiveRecord , based on the available columns for the table
“users” in the database.

HTH,

Peter

5

Thank you, but I knew that, I did that (use self to do what I want)
before
I asked the question.

I’d just like to know why can’t I use @first_name instead of
self.first_name, to me it seems like the same thing inside the model.

On Mon, Jan 30, 2012 at 6:25 PM, Peter V.

6

I thought they where attr_accessor method.

Thank you for clearing things up for me.

On Monday, January 30, 2012, Peter V. [email protected]
wrote:

On Mon, Jan 30, 2012 at 9:59 PM, Rodrigo R. [email protected]
wrote:

Thank you, but I knew that, I did that (use self to do what I want)
before I asked the question.
I’d just like to know why can’t I use @first_name instead of
self.first_name, to me it seems like the same thing inside the model.

They are not:
@first_name is an “instance variable”. You could set it like this:
@first_name = user.first_name
but it is not automatically set, and it is also not typically used like
that.

You received this message because you are subscribed to the Google G.
“Ruby on Rails: Talk” group.
To post to this group, send email to [email protected].
To unsubscribe from this group, send email to
[email protected].
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

7

On Jan 31, 2:29am, Rodrigo R. [email protected] wrote:

I thought they where attr_accessor method.

Thank you for clearing things up for me.

To add a little more info, the attribute values are stored in the
@attributes / @attributes_cache hashes

Fred