When do you use 'self' inside of a Model?

I’m a little confused when I should be using ‘self’ in my model.

I had code like:

class User < ActiveRecord::Base

before_save :do_something

def do_something

self.user_bio_text = …

self.user_bio_text
end

end

If I removed ‘self’, it didn’t seem to set the model’s attribute at all
(it
would return nil).

I can’t recall exaclty where this happenend in my code, but I remember
that
I was trying to get the a model’s attribute and it didn’t work when I
used
‘self.some_attribute’.

So I’m confused, when do I use ‘self’ and when’t don’t I?

On May 4, 8:34pm, S Ahmed [email protected] wrote:

self.user_bio_text = …

self.user_bio_text
end

end

If I removed ‘self’, it didn’t seem to set the model’s attribute at all (it
would return nil).

Ruby doesn’t know whether foo = blah means set the local variable foo
or call your foo= accessor method and default to creating the local
variable, so if you did want to call the accessor method you need to
disambiguate it, with self.foo =

Fred

On Thu, May 5, 2011 at 3:34 AM, S Ahmed [email protected] wrote:

If I removed ‘self’, it didn’t seem to set the model’s attribute at all (it
would return nil).

when assigning values to attributes of an instance object, you need to
use
self, ie self.attribute = something.
if you’re only getting the value of that attribute, no need to add self.

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ah I see, this is what I have experienced.

But why is that? Shouldn’t both getting and setting have similiar
behaviour?

I think when I was getting a value, using self.attribute wasn’t working,
is
that the case or was I doing somehting else wrong?

On May 5, 2:41am, S Ahmed [email protected] wrote:

ah I see, this is what I have experienced.

But why is that? Shouldn’t both getting and setting have similiar
behaviour?

I think when I was getting a value, using self.attribute wasn’t working, is
that the case or was I doing somehting else wrong?

There is the same ambiguity when getting a value, however (unlike when
setting)
if there is no local variable called foo then ruby can assume that foo
means self.foo.
If there was such a local variable then you’d need to disambiguate in
the same way

Fred

On Thu, May 5, 2011 at 9:41 AM, S Ahmed [email protected] wrote:

ah I see, this is what I have experienced.

But why is that? Shouldn’t both getting and setting have similiar
behaviour?

I think when I was getting a value, using self.attribute wasn’t working, is
that the case or was I doing somehting else wrong?

when you want to get a value, you can use self or not but it should
return
the same value unless, as Fred pointed out, you set
a local variable with the same name as one of the instance object’s
attribute where using self.attribute would return the
attribute value, and using attribute (which is also the local variable
name)
would return the variable value.

I had code like:
self.user_bio_text

So I’m confused, when do I use ‘self’ and when’t don’t I?

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got it.

I just want to understand, why is it different when setting a value, why
doesn’t it assume I want self.attribute1 if there was no local variable
with
the same name e.g. ‘attribute1’.

On Thu, May 5, 2011 at 2:00 AM, Frederick C.
<[email protected]

On 5 May 2011 15:23, S Ahmed [email protected] wrote:

I just want to understand, why is it different when setting a value, why
doesn’t it assume I want self.attribute1 if there was no local variable with
the same name e.g. ‘attribute1’.

How would you ever create that attribute1 local variable if the
setting assumed it should use self.attribute1 ?! :slight_smile:

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