Class variables in an inheritance hierarchy


#1

Assume the following structure:

class Base
end

class Account < Base
end

class Opportunity < Base
end

I want to have a class variable Account.fields that is different than
Opportunity.fields, so that all instances of Account can reference the
Account.fields and all instances if Opportunity can reference
Opportunity.fields and get the correct results.

As a reference, I am trying to create something akin to ActiveRecord
(for a
different type of datasource) where each distinct object has it’s own
set of
attributes. I’ve been looking at the ActiveRecord code, but being new to
Ruby it’s giving me a bit of a headache :slight_smile:

Thanks!

Todd B.


#2

Hi –

On Sat, 21 Jan 2006, Todd B. wrote:

I want to have a class variable Account.fields that is different than
Opportunity.fields, so that all instances of Account can reference the
Account.fields and all instances if Opportunity can reference
Opportunity.fields and get the correct results.

Account.fields and Opportunity fields are methods, not variables. You
can easily define them:

class Account < Base
def self.fields
# code here, possibly using instance variable to hold info
end

etc.

end

Or you could put it in a module and extend the various classes with
it. (The best exact way will depend on what’s in the method.)

For the instances:

class Base
def fields
self.class.fields
end
end

That way, each object will know to query its own class to get the
right fields method.

David


David A. Black
removed_email_address@domain.invalid

“Ruby for Rails”, from Manning Publications, coming April 2006!


#3

Todd B. wrote:

Assume the following structure:

class Base
end

class Account < Base
end

class Opportunity < Base
end

I want to have a class variable Account.fields that is different than
Opportunity.fields, so that all instances of Account can reference the
Account.fields and all instances if Opportunity can reference
Opportunity.fields and get the correct results.

As a reference, I am trying to create something akin to ActiveRecord
(for a
different type of datasource) where each distinct object has it’s own
set of
attributes. I’ve been looking at the ActiveRecord code, but being new to
Ruby it’s giving me a bit of a headache :slight_smile:

You can use class instance variables (Classes Are Objects Too™ :slight_smile:

class Account < Base
# We are in the context of the class so this variable
# will belong to the class, not its instances.
@fields = something
end

You would also need to set up accessors for the variables.

Thanks!

Todd B.

E