Overriding object instantiation?

Rails
1

Hi all,

ROR newbie coming from a PHP background here.

I have a model that inherits from ActiveRecord::Base. I would like to
extend that into two further models, to separate functionality from
each other. Basically:

class Person < ActiveRecord::Base
attr_accessible :gender
end

class Male < Person

end

class Female < Person

end

How can I write a method within Person that will detect what gender
has been defined and return the proper object based on it?

I’m thinking something like…

def self.new
gender_class = self.gender == ‘Female’ ? ‘Female’ : ‘Male’
eval(gender_class).new
end

In that version, though, “self.gender” isn’t recognized. I’m sure I’m
missing something really basic, but can someone point out what it is?

Thanks!

2

moonshadow wrote:

Hi all,

ROR newbie coming from a PHP background here.

I have a model that inherits from ActiveRecord::Base. I would like to
extend that into two further models, to separate functionality from
each other. Basically:

class Person < ActiveRecord::Base
attr_accessible :gender
end

class Male < Person

end

class Female < Person

end

How can I write a method within Person that will detect what gender
has been defined and return the proper object based on it?

You probably want to use single-table inheritance (STI) for this. Read
the ActiveRecord docs on this point.

Best,

Marnen Laibow-Koser
http://www.marnen.org
[email protected]

3

On Sep 14, 11:31 am, moonshadow [email protected] wrote:

In that version, though, “self.gender” isn’t recognized. I’m sure I’m
missing something really basic, but can someone point out what it is?

new is a class method, but gender is an instance method. Apart from
that I’m not sure what you’re trying to do? Do you know that Active
Record can handle STI for you ?

Fred

4

moonshadow wrote:

def self.new
gender_class = self.gender == ‘Female’ ? ‘Female’ : ‘Male’
eval(gender_class).new
end

Really, look into how ActiveRecord handles STI by using the type column.
It will handle all of this for you.

That said, the way to do something when an object is created is with:

def initialize

do some stuff, and you should probably call super

super
end

5

if you put a field called type in the table of the base class AR will
automaticly save to the correct class, in fact from that moment on
everything will behave as is you had 2 models, no need for more
configuration.

On Tue, Sep 14, 2010 at 10:20 AM, Frederick C. <