Overriding default ActiveRecord getter and setter

Hi,

I have two ActiveRecord classes, Player and User. Both underlying
tables have a column called email.

class User < ActiveRecord::Base
end

class Player < ActiveRecord::Base
  belongs_to :user
end

If the player instance's user attribute is not nil I want any reference
to player.email get or set player.user.email - so I tried this...

class Player < ActiveRecord::Base
  belongs_to :user
  def email
    return user.email if !(user.nil? || user.empty?)
  end
end

... but it doesn't work. When I retreive a relevant player object and
try player.email I still get the email address from the player rather
than the user.

Any ideas where I am going wrong?

Martin

Martin,

Try this:

def email
  user ? user.email : self[:email]
end

Zack,

I added...

  def email
  user ? user.email : self[:email]
  end

  def email=(email)
    (user ? user : self).email = email
  end

This still doesn't work, it still brings back the player.email value.

Strangely it does work in console.

Martin

I can reproduce the same behaviour in console by doing

p = Player.find 4
p.email => "user-email@dot.com" # what i want
p[:email] => "player-email@dot.com" # not what i want

So are forms populated using second approach?

If so this seems to negate accessor overloading as far as form handling
is concerned.

Martin

I can reproduce the same behaviour in console by doing

p = Player.find 4
p.email => "user-email@dot.com" # what i want
p[:email] => "player-email@dot.com" # not what i want

So are forms populated using second approach?

If so this seems to negate accessor overloading as far as form handling
is concerned.

Martin

> Zack,
>
> I added...
>
> def email
> user ? user.email : self[:email]
> end
>
> def email=(email)
> (user ? user : self).email = email
> end
>
> This still doesn't work, it still brings back the player.email value.
>
> Strangely it does work in console.
>
> Martin
>
>
>
> > > Hi,
>
> > > I have two ActiveRecord classes, Player and User. Both underlying
> > > tables have a column called email.
>
> > > class User < ActiveRecord::Base
> > > end
>
> > > class Player < ActiveRecord::Base
> > > belongs_to :user
> > > end
>
> > > If the player instance's user attribute is not nil I want any reference
> > > to player.email get or set player.user.email - so I tried this...
>
> > > class Player < ActiveRecord::Base
> > > belongs_to :user
> > > def email
> > > return user.email if !(user.nil? || user.empty?)
> > > end
> > > end
>
> > > ... but it doesn't work. When I retreive a relevant player object and
> > > try player.email I still get the email address from the player rather
> > > than the user.
>
> > > Any ideas where I am going wrong?
>
> > > MartinMartin,
>
> > Try this:
>
> > def email
> > user ? user.email : self[:email]
> > end
>
> > --
> > Zack Chandlerhttp://depixelate.comhttp://trackplace.com

>

Martin,

p.email => "user-email@dot.com" # what i want

This is good.

p[:email] => "player-email@dot.com" # not what i want

This is not good because it bypasses the accessor that you just wrote.
The reason is ActiveRecord::Base overrides [] like this:

      def [](attr_name)
        read_attribute(attr_name)
      end

... so it reads the actual column data. Use the first approach.

Hope this helps.

Zack,

In console I have the choice to use p.email, but when my form displays
it is still showing the data from the player object, bypassing my
overridden method.

I assume that <%= text_field 'player', 'email' %> must effectively
still call read_attribute(attr_name) rather than use the accessor.

Martin

I think I may have found an answer to this, but it doesn't seem write.

If I override the player_before_type_cast and player_before_type_cast=
methods it works, as this is what the form calls to get the values to
display?

This works, but its it 'right'?

Martin

The problem is that text_field uses *_before_type_cast accessors to get data.
I see two solutions:
  1. overriding *_before_type_cast accessor (as you described)
  2. adding virtual field (that has no underlying column). E.g. in your case
this could be done like this:

  class Player
    def user_or_player_email
      return user.email if user
      self.email
    end
    def user_or_player_email=(value)
      self.email = value
    end
  end

The trick here is that text_field will use plain value (not _before_type_cast
variant) if attribute doesn't support _before_type_cast accessor.

Although, I would prefer using second variant.

You could rename players.email column to something like "custom_email"
or "player_email" and use "email" as the name of virtual attribute.

No, dynamically generated accessors for DB columns do not overwrite existing
accessors. Dynamic accessor don't get generated if there is method with the
same name already.