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Handle enabling/disabling observers at different levels of the class …
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…hierarchy.

Last call wins.
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@myronmarston @dhh
myronmarston authored and dhh committed Apr 28, 2011
1 parent 1f8cc44 commit ad62f19
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Showing 3 changed files with 75 additions and 3 deletions.
34 changes: 31 additions & 3 deletions activemodel/lib/active_model/observer_array.rb
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Expand Up @@ -48,7 +48,7 @@ def enable(*observers, &block)
set_enablement(true, observers, &block) set_enablement(true, observers, &block)
end end


private protected


def observer_class_for(observer) def observer_class_for(observer)
return observer if observer.is_a?(Class) return observer if observer.is_a?(Class)
Expand All @@ -61,13 +61,37 @@ def observer_class_for(observer)
end end
end end


def start_transaction
disabled_observer_stack.push(disabled_observers.dup)
each_subclass_array do |array|
array.start_transaction
end
end

def disabled_observer_stack
@disabled_observer_stack ||= []
end

def end_transaction
@disabled_observers = disabled_observer_stack.pop
each_subclass_array do |array|
array.end_transaction
end
end

def transaction def transaction
orig_disabled_observers = disabled_observers.dup start_transaction


begin begin
yield yield
ensure ensure
@disabled_observers = orig_disabled_observers end_transaction
end
end

def each_subclass_array
model_class.subclasses.each do |subclass|
yield self.class.for(subclass)
end end
end end


Expand All @@ -92,6 +116,10 @@ def set_enablement(enabled, observers)
disabled_observers << klass disabled_observers << klass
end end
end end

each_subclass_array do |array|
array.set_enablement(enabled, observers)
end
end end
end end
end end
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5 changes: 5 additions & 0 deletions activemodel/lib/active_model/observing.rb
View file
Expand Up @@ -70,6 +70,10 @@ def count_observers
observer_instances.size observer_instances.size
end end


def subclasses

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@josevalim

josevalim Apr 28, 2011

Contributor

This is going to leak memory like crazy in development.

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@josevalim

josevalim Apr 28, 2011

Contributor

Instead of keeping the subclasses to propagate changes, make the subclass ask the parent if something is disabled or not. I am going to revert this commit temporarily until a better fix is provided.

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@myronmarston

myronmarston Apr 28, 2011

Author Contributor

I didn't really think through class reloading in development :(.

That said, I'm not sure how your proposed change would work. The reason I added this to keep track of the subclasses is because @dhh wanted last call to win, so in a case like:

Post.observers.disable :all

#... later
ActiveRecord::Base.observers.enable :all

...the desired behavior is that the enable :all on AR::Base will propagate to subclasses since it was called last. I'm not sure how to do that without keeping track of subclasses.

Do either of you have a recommendation for a different implementation to achieve the desired behavior?

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@josevalim

josevalim Apr 28, 2011

Contributor

Right. If you really need to use descendants, use ActiveSupport::DescendantsTracker that will handle class reloading on development for you. When sending a pull request, remember to revert my revert first. :) Thanks for looking into this!

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@myronmarston

myronmarston Apr 28, 2011

Author Contributor

If you really need to use descendants, use ActiveSupport::DescendantsTracker that will handle class reloading on development for you.

Thanks for the tip! I didn't even know about DescendantsTracker. Since AR::Base is already extending that module and also includes ActiveModel::Observing, I was thinking I should remove it from AR::Base and extend it in the included hook of ActiveModel::Observing so that AR::Base doesn't get it twice, and every includer of ActiveModel::Observing will get it. Is that the right approach?

This conversation made me think that maybe some of the code in my prior commit will have the same kind of leaking problem:

https://github.com/rails/rails/blob/1f8cc446d9a7ab751a2def65309ac4bc71e85cd3/activemodel/lib/active_model/observer_array.rb#L7-14

The INSTANCES hash keeps track of the ObserverArray instance for a given model class, and makes it easy to get the instance using the for class method. This could potentially have the same kind of memory leaking issues in development, I think...but I've got an idea for how to keep the same behavior without needing the hash, though.

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@josevalim

josevalim Apr 28, 2011

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Right. DescendantsTracker is also included in AS::Callbacks so it will be included several times anyway. We just need to be careful to not do a lot of work in the self.included hook of DescendantsTracker, because that will certainly be executed more than once.

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@myronmarston

myronmarston Apr 28, 2011

Author Contributor

@josevalim: I have it fixed in my am_disabling_fix_memory_leaks branch (along with a fix for another bug I just noticed!), but I'm getting a 500 error from github when I try to open a pull request. Can you merge that in?

Thanks for helping me make this code even better :).

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@josevalim

josevalim Apr 28, 2011

Contributor

Done! Thanks for your work!
@subclasses ||= []
end

protected protected
def instantiate_observer(observer) #:nodoc: def instantiate_observer(observer) #:nodoc:
# string/symbol # string/symbol
Expand All @@ -89,6 +93,7 @@ def instantiate_observer(observer) #:nodoc:
# Notify observers when the observed class is subclassed. # Notify observers when the observed class is subclassed.
def inherited(subclass) def inherited(subclass)
super super
subclasses << subclass
notify_observers :observed_class_inherited, subclass notify_observers :observed_class_inherited, subclass
end end
end end
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39 changes: 39 additions & 0 deletions activemodel/test/cases/observer_array_test.rb
View file
Expand Up @@ -118,5 +118,44 @@ def assert_observer_not_notified(model_class, observer_class)
ORM.observers.disable Widget ORM.observers.disable Widget
end end
end end

test "allows #enable at the superclass level to override #disable at the subclass level when called last" do
Widget.observers.disable :all
ORM.observers.enable :all

assert_observer_notified Widget, WidgetObserver
assert_observer_notified Budget, BudgetObserver
assert_observer_notified Widget, AuditTrail
assert_observer_notified Budget, AuditTrail
end

test "allows #disable at the superclass level to override #enable at the subclass level when called last" do
Budget.observers.enable :audit_trail
ORM.observers.disable :audit_trail

assert_observer_notified Widget, WidgetObserver
assert_observer_notified Budget, BudgetObserver
assert_observer_not_notified Widget, AuditTrail
assert_observer_not_notified Budget, AuditTrail
end

test "can use the block form at different levels of the hierarchy" do
yielded = false
Widget.observers.disable :all

ORM.observers.enable :all do
yielded = true
assert_observer_notified Widget, WidgetObserver
assert_observer_notified Budget, BudgetObserver
assert_observer_notified Widget, AuditTrail
assert_observer_notified Budget, AuditTrail
end

assert yielded
assert_observer_not_notified Widget, WidgetObserver
assert_observer_notified Budget, BudgetObserver
assert_observer_not_notified Widget, AuditTrail
assert_observer_notified Budget, AuditTrail
end
end end


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