There are several issues with each of the available methods, but I believe that defining an after_initialize
callback is the way to go for the following reasons:
default_scope
will initialize values for new models, but then that will become the scope on which you find the model. If you just want to initialize some numbers to 0 then this is not what you want.- Defining defaults in your migration also works part of the time… As has already been mentioned this will not work when you just call Model.new.
- Overriding
initialize
can work, but don’t forget to callsuper
! - Using a plugin like phusion’s is getting a bit ridiculous. This is ruby, do we really need a plugin just to initialize some default values?
- Overriding
after_initialize
is deprecated as of Rails 3. When I overrideafter_initialize
in rails 3.0.3 I get the following warning in the console:
DEPRECATION WARNING: Base#after_initialize has been deprecated, please use Base.after_initialize :method instead. (called from /Users/me/myapp/app/models/my_model:15)
Therefore I’d say write an after_initialize
callback, which lets you default attributes in addition to letting you set defaults on associations like so:
class Person < ActiveRecord::Base
has_one :address
after_initialize :init
def init
self.number ||= 0.0 #will set the default value only if it's nil
self.address ||= build_address #let's you set a default association
end
end
Now you have just one place to look for initialization of your models. I’m using this method until someone comes up with a better one.
Caveats:
-
For boolean fields do:
self.bool_field = true if self.bool_field.nil?
See Paul Russell’s comment on this answer for more details
-
If you’re only selecting a subset of columns for a model (ie; using
select
in a query likePerson.select(:firstname, :lastname).all
) you will get aMissingAttributeError
if yourinit
method accesses a column that hasn’t been included in theselect
clause. You can guard against this case like so:self.number ||= 0.0 if self.has_attribute? :number
and for a boolean column…
self.bool_field = true if (self.has_attribute? :bool_value) && self.bool_field.nil?
Also note that the syntax is different prior to Rails 3.2 (see Cliff Darling’s comment below)