Federation: Triggering Update Activities

I need to update backlinks in two cases:

• When the url is changed (#237 )
• When I change the value of a one-to-many or one-to-one relationship

As I'm not able to access the old value in Django without storing it, this information will need to be deduced sender or receiver side

As a solution I propose using a subscription-based solution like with DjangoLDP-Notifications.

• Whenever I create a backlink I follow-up by sending a request to subscribe to it
• Whenever the resource is saved, I send the Update notification to all subscribers on the resource

This solution is clean, but a little greedy with bandwidth. It could be made to use less bandwidth by having the sender register/unregister the subscription when the backlink is generated, so the receiver need not request it. Having an endpoint to register a subscription has the added benefit that third parties can subscribe to changes on the model

What do you think @jbpasquier @sylvain @balessan ? I suppose this would raise the question of integrating DjangoLDPNotifications into DjangoLDP again

TODO:

• backlinks subscription service
• permissions for subscriptions.. #236
• possible integration with DjangoLDP-Notifications

changed milestone to %0.7

changed the description

added need spec label

mentioned in issue management/core-team#3

changed the description

removed need spec label

@jbpasquier @sylvain @balessan UP :)

• Whenever I create a backlink I follow-up by sending a request to subscribe to it
• Whenever the resource is saved, I send the Update notification to all subscribers on the resource

This is fine

having the sender register/unregister the subscription

I'm a bit concerned with server shutdown/unreachable because of the un-registering part of this.

Having an endpoint to register a subscription has the added benefit that third parties can subscribe to changes on the model

But this is pretty cool, handling subscription creation from external parties could allow some cool stuff. Permissions must be handled before having this though.

changed the description

marked the checklist item backlinks subscription service as completed

added 6h 25m of time spent at 2020-05-20

mentioned in merge request !160 (merged)