CODEWITHSUNDEEP
core-datarestkitkey-value-observing
ptc
ptc

Reputation: 734

iOS KVO and NSManagedObject - fine grained mechanism for detecting changes

I have a background process receiving and applying changes to Core Data entities from a back end server using Restkit which works really well. All the entities have a version number property which updates when the back end accepts changes and publishes a new version. If an entity the user is viewing is changed I need to update the view with the latest version information.

Using KVO to observe version number for the current entity and refreshing the view when it changes works really well as long as version number is the last property.

That is, the 'column order' matters, and property updates are atomic. If the version number is the last property then when the observer is invoked all changes to all entity properties will have been applied.

If version number is not the last property defined, then when the observer is invoked the updated values of the properties after version will not been applied.

The solution is to change the database and ensure that version number is always last. This works however I cannot find anything in the documentation to suggest that the sequence of property changes is guaranteed.

I assume the only way to get a water-tight non-atomic notification is to register for managed object context change notifications and then process those notifications looking for changes to objects of interest. My concern with this is that it is not fined grained and there will be a lot of unnecessary processing to find relatively few things of interest.

Is this correct or is there a way to ensure an non-atomic view of an object when using KVO?

Upvotes: 1

Views: 685

Answers (1)

Wain
Wain

Reputation: 119041

If you wanted to use KVO you would need to layer some change management on top, such as when the managed object is saved you check the version number and change another (non-persistent) attribute that is being observed. You can be sure that everything has been updated in a logical set when the object is saved.

Generally the context save notification is the approved approach. So long as you aren't making thousands of changes or making few large saves to the context it shouldn't be an issue. You can also look at using predicates to filter the changes and / or a fetched results controller (which does the observation for you).

Upvotes: 1

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