Rails - Apr 2007 - Beginner question - overwrite a value in a model

Hi,

i am trying to overwrite a value in a model so that
the new value is beeing saved in the database instead of the one the
user
typed into the form.

this is my controller

class Movie < ActiveRecord::Base

  def self.creation_date=(a)
    self.creation_date = "2000-01-01"
  end

end

(it''s only some testing for getting a feeling for the basic way
ror works...)

the create form is generated by the standard scaffold :movie
in my admin controller.

the new movie is beeing created but it uses the value
from the form, not my new "overwritten" one.

it''s obviously a simple question but iam stucked now for
about 2.5 houres :( shame on me...

any ideas?

Greetings,

Pascal


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> any ideas?
Try writing your overwrite code in the after_update or after_save 
callback method.  In this method, write straight to the database via 
something like:

def after_update
  model.connection.execute( "UPDATE model set creation_date=now() WHERE 
id=" << model.id)
end

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

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> Hi,
>
> i am trying to overwrite a value in a model so that
> the new value is beeing saved in the database instead of the one the
> user
> typed into the form.
>
> this is my controller
I think you meant model...  anyway...

class Movie < ActiveRecord::Base

before_save :fudge_creation_date

...

def fudge_creation_date
 	self.creation_date = Date.parse(''2001-01-1'')
end

end

Then every time you save the record it will do what you want.
>
> class Movie < ActiveRecord::Base
>
>  def self.creation_date=(a)
>    self.creation_date = "2000-01-01"
>  end
>
> end
>
> (it''s only some testing for getting a feeling for the basic way
> ror works...)
>
> the create form is generated by the standard scaffold :movie
> in my admin controller.
>
> the new movie is beeing created but it uses the value
> from the form, not my new "overwritten" one.
>
> it''s obviously a simple question but iam stucked now for
> about 2.5 houres :( shame on me...
>
> any ideas?
>
> Greetings,
>
> Pascal
>
>
> >
>
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thanks (yes, model, not controller :) ),

but why does it work in the example at "agile webdevelopement with
ror"
at the model
http://media.pragprog.com/titles/rails2/code/depot_p/app/models/user.rb

they are setting the hashed_password value in the password=(pwd)
method.


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On Wed, Apr 18, 2007 at 13:55 -0700, Pascal Friederich
wrote:
> class Movie < ActiveRecord::Base
> 
>   def self.creation_date=(a)
>     self.creation_date = "2000-01-01"
>   end
> 
> end
# skipped
> the new movie is beeing created but it uses the value
> from the form, not my new "overwritten" one.
maybe 
    # instance method should be without `self.` prefix!
    def creation_date=(a)
        self[:creation_date] = "2000-01-01"
    end

?

-- 
wbr, sh0ckfile.
FileForum moders team
http://www.fforum.ru

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> >   def self.creation_date=(a)
> >     self.creation_date = "2000-01-01"
> >   end
Notice that when you add self.some_method you are creating a "Class"
method rather than an "Instance" method.

def password=(pwd)
    @password = pwd
    return if pwd.blank?
    create_new_salt
    self.hashed_password = User.encrypted_password(self.password,
self.salt)
  end

private

  def self.encrypted_password(password, salt)
    string_to_hash = password + "wibble" + salt  #
''wibble'' makes it
harder to guess
    Digest::SHA1.hexdigest(string_to_hash)
  end

See how the AWDWR book is defining the "password=(pwd)" method to be
an instance method (no self.)

User.encrypted_password(..., ...) is defined as a Class method.
Notice how they call the class method on the class not a reference to
an instance.

On Apr 18, 5:31 pm, Sh0Ck_filE
<sh0ckf...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> On Wed, Apr 18, 2007 at 13:55 -0700, Pascal Friederich wrote:
> > class Movie < ActiveRecord::Base
>
> >   def self.creation_date=(a)
> >     self.creation_date = "2000-01-01"
> >   end
>
> > end
> # skipped
> > the new movie is beeing created but it uses the value
> > from the form, not my new "overwritten" one.
>
> maybe
>     # instance method should be without `self.` prefix!
>     def creation_date=(a)
>         self[:creation_date] = "2000-01-01"
>     end
>
> ?
>
> --
> wbr, sh0ckfile.
> FileForum moders teamhttp://www.fforum.ru

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I''m also curious why you want all your creation dates to be
"2000-01-01," without any way to change it?

What are you really wanting to do here?  Are you looking for behavior
that time stamps record creation?  If so then Rails will happily do
that automatically for you.  All you need to do is name your column
created_on and it will automatically be set by the framework to the
current date.  You can also use created_at to get a full date and
time,  update_on/updated_at to have a time stamp update every time the
record changes.

On Apr 18, 6:22 pm, Robert Walker
<rwalker...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> > >   def self.creation_date=(a)
> > >     self.creation_date = "2000-01-01"
> > >   end
>
> Notice that when you add self.some_method you are creating a
"Class"
> method rather than an "Instance" method.
>
> def password=(pwd)
>     @password = pwd
>     return if pwd.blank?
>     create_new_salt
>     self.hashed_password = User.encrypted_password(self.password,
> self.salt)
>   end
>
> private
>
>   def self.encrypted_password(password, salt)
>     string_to_hash = password + "wibble" + salt  #
''wibble'' makes it
> harder to guess
>     Digest::SHA1.hexdigest(string_to_hash)
>   end
>
> See how the AWDWR book is defining the "password=(pwd)" method to
be
> an instance method (no self.)
>
> User.encrypted_password(..., ...) is defined as a Class method.
> Notice how they call the class method on the class not a reference to
> an instance.
>
> On Apr 18, 5:31 pm, Sh0Ck_filE
<sh0ckf...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > On Wed, Apr 18, 2007 at 13:55 -0700, Pascal Friederich wrote:
> > > class Movie < ActiveRecord::Base
>
> > >   def self.creation_date=(a)
> > >     self.creation_date = "2000-01-01"
> > >   end
>
> > > end
> > # skipped
> > > the new movie is beeing created but it uses the value
> > > from the form, not my new "overwritten" one.
>
> > maybe
> >     # instance method should be without `self.` prefix!
> >     def creation_date=(a)
> >         self[:creation_date] = "2000-01-01"
> >     end
>
> > ?
>
> > --
> > wbr, sh0ckfile.
> > FileForum moders teamhttp://www.fforum.ru

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thanks for the, i think i understood this now :)

but the thing that makes me pain in my brain is that
self.hashed_password = User.encrypted...xxx
asignment is to self.hashed_password and it works, the value
that is written to the table at the "hashed_password" column is the
one returned from user.encrypted...xxx.

it is functional equal to my new method which doesn''t work
(the solution with bevore_save does work but that doesn''t solve the
riddle the AWDWROR from book example in comparison to my
little method)

def creation_date=(cd)
  #same as self.hashed_password = ... // like AWDWROR team does
  self.creation_date = Date.parse(''2000-01-01'')
end

(sorry for my bad / hard to read english sentences.. :( )

On 19 Apr., 00:22, Robert Walker
<rwalker...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> > >   def self.creation_date=(a)
> > >     self.creation_date = "2000-01-01"
> > >   end
>
> Notice that when you add self.some_method you are creating a
"Class"
> method rather than an "Instance" method.
>
> def password=(pwd)
>     @password = pwd
>     return if pwd.blank?
>     create_new_salt
>     self.hashed_password = User.encrypted_password(self.password,
> self.salt)
>   end
>
> private
>
>   def self.encrypted_password(password, salt)
>     string_to_hash = password + "wibble" + salt  #
''wibble'' makes it
> harder to guess
>     Digest::SHA1.hexdigest(string_to_hash)
>   end
>
> See how the AWDWR book is defining the "password=(pwd)" method to
be
> an instance method (no self.)
>
> User.encrypted_password(..., ...) is defined as a Class method.
> Notice how they call the class method on the class not a reference to
> an instance.

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this is realy nice.
and in fact, this was one of the things i tried to figure out.
awsome!

the other thing is that i just wanted to now -if- (ok i was really
shure
it -is-) i can and -how- i can set values to a dynamic / static
default
value inside a model.

as you see, iam really new to ruby (and the mvc idear in general..)
where do -you- find such things like the "created_on and it will
automatically"
trick? Ok, api will provide these information but a) it find it
difficult to read and
b) how to find s.th. you dont even know it exists? :)

On 19 Apr., 00:30, Robert Walker
<rwalker...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> I''m also curious why you want all your creation dates to be
> "2000-01-01," without any way to change it?
>
> What are you really wanting to do here?  Are you looking for behavior
> that time stamps record creation?  If so then Rails will happily do
> that automatically for you.  All you need to do is name your column
> created_on and it will automatically be set by the framework to the
> current date.  You can also use created_at to get a full date and
> time,  update_on/updated_at to have a time stamp update every time the
> record changes.
>
> On Apr 18, 6:22 pm, Robert Walker
<rwalker...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > > >   def self.creation_date=(a)
> > > >     self.creation_date = "2000-01-01"
> > > >   end
>
> > Notice that when you add self.some_method you are creating a
"Class"
> > method rather than an "Instance" method.
>
> > def password=(pwd)
> >     @password = pwd
> >     return if pwd.blank?
> >     create_new_salt
> >     self.hashed_password = User.encrypted_password(self.password,
> > self.salt)
> >   end
>
> > private
>
> >   def self.encrypted_password(password, salt)
> >     string_to_hash = password + "wibble" + salt  #
''wibble'' makes it
> > harder to guess
> >     Digest::SHA1.hexdigest(string_to_hash)
> >   end
>
> > See how the AWDWR book is defining the "password=(pwd)"
method to be
> > an instance method (no self.)
>
> > User.encrypted_password(..., ...) is defined as a Class method.
> > Notice how they call the class method on the class not a reference to
> > an instance.
>
> > On Apr 18, 5:31 pm, Sh0Ck_filE
<sh0ckf...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > > On Wed, Apr 18, 2007 at 13:55 -0700, Pascal Friederich wrote:
> > > > class Movie < ActiveRecord::Base
>
> > > >   def self.creation_date=(a)
> > > >     self.creation_date = "2000-01-01"
> > > >   end
>
> > > > end
> > > # skipped
> > > > the new movie is beeing created but it uses the value
> > > > from the form, not my new "overwritten" one.
>
> > > maybe
> > >     # instance method should be without `self.` prefix!
> > >     def creation_date=(a)
> > >         self[:creation_date] = "2000-01-01"
> > >     end
>
> > > ?
>
> > > --
> > > wbr, sh0ckfile.
> > > FileForum moders teamhttp://www.fforum.ru

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Pascal,

1) self.hashed_password = User.encrypted...xxx
2) asignment is to self.hashed_password and it works, the value

Here''s the bit that you are missing. In line 1 above
self.hashed_password is NOT the definition of the hashed_password
method.

You do not see something like:

def self.hashed_password
  ...
  ...
end

the hashed_password is an instance method (not a class method) that is
added to the User model by Rails.

def self.authenticate(name, password)
  user = self.find_by_name(name)     # <=== geting a reference to an
instance of User
  if user
    expected_password = encrypted_password(password, user.salt)
    if user.hashed_password != expected_password    # <=== referencing
hashed_password on an instance of User
      user = nil
    end
  end
  user
end

On Apr 18, 6:31 pm, Pascal Friederich
<pau...-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>
wrote:
> thanks for the, i think i understood this now :)
>
> but the thing that makes me pain in my brain is that
> self.hashed_password = User.encrypted...xxx
> asignment is to self.hashed_password and it works, the value
> that is written to the table at the "hashed_password" column is
the
> one returned from user.encrypted...xxx.
>
> it is functional equal to my new method which doesn''t work
> (the solution with bevore_save does work but that doesn''t solve
the
> riddle the AWDWROR from book example in comparison to my
> little method)
>
> def creation_date=(cd)
>   #same as self.hashed_password = ... // like AWDWROR team does
>   self.creation_date = Date.parse(''2000-01-01'')
> end
>
> (sorry for my bad / hard to read english sentences.. :( )
>
> On 19 Apr., 00:22, Robert Walker
<rwalker...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
> > > >   def self.creation_date=(a)
> > > >     self.creation_date = "2000-01-01"
> > > >   end
>
> > Notice that when you add self.some_method you are creating a
"Class"
> > method rather than an "Instance" method.
>
> > def password=(pwd)
> >     @password = pwd
> >     return if pwd.blank?
> >     create_new_salt
> >     self.hashed_password = User.encrypted_password(self.password,
> > self.salt)
> >   end
>
> > private
>
> >   def self.encrypted_password(password, salt)
> >     string_to_hash = password + "wibble" + salt  #
''wibble'' makes it
> > harder to guess
> >     Digest::SHA1.hexdigest(string_to_hash)
> >   end
>
> > See how the AWDWR book is defining the "password=(pwd)"
method to be
> > an instance method (no self.)
>
> > User.encrypted_password(..., ...) is defined as a Class method.
> > Notice how they call the class method on the class not a reference to
> > an instance.

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