load_association_classes can block migrations (and slow down script/runner)

[cainlevy]

Hello,

I ran into a problem recently that was previously reported as ticket
#802 [1]. The issue, briefly, occurs when a model definition runs a
class method (such as for a plugin) that checks table information. In
this case, loading the model requires the database table to already
exist. Running `rake db:migrate` in staging or production (anywhere
with config.cache_classes=true) will then try and eager load all
application classes, quickly failing with a table-not-found sort of
error.

Also, the eager loading seems pretty detrimental any time Rails is
booted from the console, such as via `script/runner` or `rake
db:migrate`. Not only can it blow up because of an unmigrated
database, but it incurs a pretty senseless performance hit for what
may be a simple task. This could really hit applications that use BJ
to run jobs in a full Rails environment, for example.

Does anyone have ideas how Rails might be smarter about when to eager
load?

-Lance

[1] http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/802

[Michael Koziarski]

> Also, the eager loading seems pretty detrimental any time Rails is
> booted from the console, such as via `script/runner` or `rake
> db:migrate`. Not only can it blow up because of an unmigrated
> database, but it incurs a pretty senseless performance hit for what
> may be a simple task. This could really hit applications that use BJ
> to run jobs in a full Rails environment, for example.
>
> Does anyone have ideas how Rails might be smarter about when to eager
> load?

This is something that's being worked on in edge rails at present.
The goal is to move that preloading code to be as 'lazy' as it can be.
The code still needs to fire in order to allow thread safe
dispatching, but there's definitely no reason to do it for rake tasks,
script/runner etc.

Josh and jeremy have been hacking away on it, perhaps they have
something to add?

> -Lance
>
> [1] http://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/802
> >
>



--
Cheers

Koz