Model references fail in the initializer


#1

I know that we shouldn’t make database calls in the Initializer, but how
do we avoid this when a class ‘bootstraps’ itself when it is required,
e.g.

class Status < ActiveRecord::Base

Add constants representing the various status

SUBMITTED = self.find(…)
APPROVED = self.find(…)
DENIED = self.find(…)
end

I have, in my initialization block, a line which causes some model
classes to be ‘required’, e.g.

config.active_record.observers = :audit_observer # ‘requires’ observed
classes

My problem is that the initialization block runs while executing
migrations, and therefore fails on a migration from version 0, because
the Status table doesn’t yet exist.

I’ve tried config.after_initialize, with no luck. Is there some other
way to do initialization only after the migrations have run?

Thanks.

Brian


#2

Hi,

On Fri, Oct 10, 2008 at 1:03 PM, Brian H.
removed_email_address@domain.invalid wrote:

I know that we shouldn’t make database calls in the Initializer, but how
do we avoid this when a class ‘bootstraps’ itself when it is required,
e.g.

class Status < ActiveRecord::Base

Add constants representing the various status

SUBMITTED = self.find(…)
APPROVED = self.find(…)
DENIED = self.find(…)
end

Do these need to be constants? How about:

class Status < ActiveRecord::Base
class << self
def submitted
@submitted ||= find(…)
end
end
end

Or, if they’re simple enough, they could just be named scopes:

class Status < ActiveRecord::Base
named_scope :submitted, :conditions => […]
end

~ j.


#3

I had thought about making them class methods; that would work. It just
seemed more proper for them to be constants.

I have at least one more place where I’m doing ‘class-load’ time DB
access. I’ll have to see if I can make it ‘lazily evaluated’.

Since the prevailing thought is that a Rails app isn’t fully initialized
until the migrations have run (thus the caution against using models in
migrations), I wonder if it would be possible to programatically
distinguish between a Rails env in which migrations had been fully run
and otherwise.

Thanks for the response.

Brian


#4

On Oct 11, 4:29 am, Brian H. removed_email_address@domain.invalid
wrote:

and otherwise.

initialization in the sense of initializers and
config.after_initialize corresponds purely to ‘have all the framework
files, plugins etc…’ been setup and initialized. It does not have
anything to do with migrations. In that sense the framework is fully
initialized before migrations are run. You might be able to play
around with the stuff in ActiveRecord::Migrations to figure out that
sort of stuff, although it feels like a better way is to just make it
not an issue.

Fred


#5

If the only time you’re worried about your code failing is during the
migration you can simply add a check to see if the table exists and if
not don’t execute the code. it’s not a very clever solution but does
the job.

On Oct 10, 4:03 pm, Brian H. removed_email_address@domain.invalid