Add Optimistic Locking

[jcoyne]

In Hyrax/ActiveFedora, we can use the Etag to do optimistic locking. Does Valkyrie have a mechanism for doing this?

See:
https://github.com/samvera/hyrax/blob/master/app/actors/hyrax/actors/optimistic_lock_validator.rb

[tpendragon]

No. I've been thinking about this lately and trying to decide what the correct mechanism for this would be. Something like AR where there's a special lock_key property which when defined will do optimistic locking?

[tpendragon]

Proposed Success Criteria:

class Resource < Valkyrie::Resource
  attribute :title
  attribute :lock_key # Reserved attribute for when you want to enable optimistic locking
end

resource_1 = persister.save(resource: Resource.new)
resource_1.lock_key # => "unique1" # Set by the persister.
resource_1.title = ["test"]
resource_2 = persister.save(resource: resource_1)
resource_2.lock_key # => "unique2" # Set by the persister.
resource_1.title = ["test2"]
persister.save(resource: resource_1) # => Valkyrie::Persistence::StaleObjectError # Raised because resource_1.lock_key does not match the lock_key in the database (resource_2.lock_key)

[tpendragon]

Alternative API:

class Resource < Valkyrie::Resource
  optimistic_locking
  attribute :title
end