I have a model where I need to calculate one of the fields when I create
a new instance. It seems to me that I should do this in the model code
and that I should override the new and/or create methods.
Is this the right approach and, if so, how can I execute the existing
method but add on my calculation?
I want something like:
def create
-Do the original create first-
field = calculated_value
save
self
end
How do I call the original create method and use the parameters passed?
Also, should I be overriding new or create or both?
Thanks for any help.
Julian
How do I call the original create method and use the parameters passed?
Also, should I be overriding new or create or both?
I’m new at this, but I think you’ll want to take a lot at callbacks.
http://api.rubyonrails.com/classes/ActiveRecord/Callbacks.html
def test(parameters)
super
end
The super method calls the original method (eg. test) in the
superclass and passes the same parameters as the originally invoked
method.
-John
–
John S.
Computing Staff - Webmaster
Kavli Institute for Theoretical Physics
University of California, Santa Barbara
[email protected]
(805) 893-6307
Neither 
Override initialize. Create calls new internally, and new calls
initialize.
class Person < ActiveRecord::Base
alias :old_initialize :initialize
def initialize(attributes = nil)
old_initialize(attributes)
# Do whatever you want in here.
end
end
Note that your customised initialize method will be called for any
Person
object that is instantiated.
-Jonathan.
Also, should I be overriding new or create or both?
overriding new should be enough since create calls new anyway.
# File vendor/rails/activerecord/lib/active_record/base.rb,
line 443
443: def create(attributes = nil)
444: if attributes.is_a?(Array)
445: attributes.collect { |attr| create(attr) }
446: else
447: attributes.reverse_merge!(scope(:create)) if scoped?
(:create)
448:
449: object = new(attributes)
450: object.save
451: object
452: end
453: end
-John
–
John S.
Computing Staff - Webmaster
Kavli Institute for Theoretical Physics
University of California, Santa Barbara
[email protected]
(805) 893-6307
Jonathan V. wrote:
Neither
Override initialize. Create calls new internally, and new calls
initialize.
Thanks Jonathan. That’s just what I needed.
Julian
Please help me understand this.
I would thing that you would be able to simply implement your own
initialize
method and perform a super inside, like this:
class Person < ActiveRecord::Base
def initialize(*args)
super(*args)
# Do whatever you want in here.
end
end
Yet this is not working for me.