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Asked: 2026-05-25T12:54:20+00:00

I can’t seem to get a clear answer for this: when you change a

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I can’t seem to get a clear answer for this: when you change a transient property, and then call save, should the NSManagedObjectContextDidSaveNotification be triggered? In my notification listener, how can I filter out these notifications that are coming from changes in transient properties?

Here’s what I’m trying to do: I want to load up a list of contacts in the main thread, and when it’s done, I want to read the images in a background thread from the address book and attach them to the contacts. This works fine on the face of it: after loading from the Contacts entity, I use a dispatch queue to loop through all the contacts, find their image in the Address Book, and save them in Contact’s “contactImage” property (which is transient). The dispatch queue then successfully reloads the tableview (on the main thread) and the images show up next to the contacts.
The problem is that if I do anything to the contact that invokes a “save” on even ONE of the managed objects (for e.g. I delete one of the contacts), the NSManagedObjectContextDidSaveNotification is invoked for ALL the contacts. I’ve found that this is because the contactImage property was changed before … commenting that the “self.contactImage = img;” line makes the issue go away. This is surprising to me, since I would have thought that the save notification would only be called for non-transient properties.

Can anyone confirm if this is expected behavior? Or am I doing something wrong? If it’s expected, how do you filter out the updates to transient properties in the NSManagedObjectContextDidSaveNotification listener? I need to do some post-processing in the listener, and I don’ want to do it needlessly for transient property updates. I’ve checked the changedValues dictionary on the NSManagedObject, but it seems to show empty inside the listener (since only transient properties changed, I’m guessing).

Thanks.

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1 Answer

  1. Editorial Team

    Yesterday,

    Transient properties have one key characteristic — they are managed. You can easily add ivars that are not managed to any NSManagedObject. If you do so, they are not subject to -save: notifications.

    A related question: Why are you using a transient ivar? They have some specialized uses; primarily, they are used to trigger property updates throughout the model; i.e. the behavior you are seeing.

    A second related question: why are you background fetching all of the images instead of lazy loading them from the Address Book? This looks like a case of premature optimization to me.

    Andrew

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