I have been requested to make my app available off-line, which means storing the data collected via Api for use when no connection available. The problem is that when a new connection is made my local data may be out of date. Also, any changes made while off-line will need to update the server.
I'm aware of a method of syncing databases so that when new connection is made the data is automatically updated both ways. However, after browsing Google I've not found a definitive method of doing this.
Can anyone help point me in the right direction?
There should be a field like a time stamp to indicate last synced time. When ever connection is online go for a fetch validate against the timestamp and update the data in offline storage.
The same way, when you have updates while offline you can set some bool value to check whether data is synced or not and sync when you are online.
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As described in https://developer.apple.com/reference/cloudkit/ckserverchangetoken, the CloudKit servers return a change token as part of the CKFetchRecordZoneChangesOperation callback response. For what set of subsequent record fetches should I include the given change token in my fetch calls?
only fetches to the zone we fetched from?
or would it apply to any fetches to the db that that zone is in? or perhaps the whole container that the db is in?
what about app extensions? (App extensions have the same iCloud user as the main app, but have a different "user" as returned by fetchUserRecordIDWithCompletionHandler:, at least in my testing) Would it be appropriate to supply a change token from the main app in a fetch call from, say, a Messages app extension? I assume not, but would love to have a documented official answer.
I, too, found the scope of CKServerChangeToken a little unclear. However, after reviewing the documentation, both CKFetchDatabaseChangesOperation and CKFetchRecordZoneChangesOperation provide and manage their own server change tokens.
This is particularly useful if you decide to follow the CloudKit workflow Dave Browning outlines in his 2017 WWDC talk when fetching changes (around the 8 minute mark).
The recommended approach is to:
1) Fetch changes for a database using CKFetchDatabaseChangesOperation. Upon receiving the updated token via changeTokenUpdatedBlock, persist this locally. This token is 'scoped' to either the private or shared CKDatabase the operation was added to. The public database doesn't offer change tokens.
2) If you receive zone IDs via the recordZoneWithIDChangedBlock in the previous operation, this indicates there are zones which have changes you can fetch with CKFetchRecordZoneChangesOperation. This operation takes in it's own unique server change token via it's rather cumbersome initializer parameter: CKFetchRecordZoneChangesOperation.ZoneConfiguration. This is 'scoped' to this particular CKRecordZone. So, again, when receiving an updated token via recordZoneChangeTokensUpdatedBlock, it needs persisting locally (perhaps with a key which relates to it's CKRecordZone.ID).
The benefit here is that it probably minimises the number of network calls. Fetching database changes first prevents making calls for each record zone if the database doesn't report any changed zone ids.
Here's a code sample from the CloudKit team which runs through this workflow. Admittedly a few of the APIs have since changed and the comments don't explicitly make it clear the 'scope' of the server change tokens.
Our app supports offline activity. Meaning we want to persist locally the creation of new core data objects as well as any modifications on existing objects. Then when the app goes online again we automatically push those changes (and any dependencies) up to the server.
I would think that RestKit would support such an operation, but currently when offline we store creations/modifications in a local cache. If I kill the app, those changes are not persisted. And also there is no attempt by RestKit to post those items to their originally intended endpoints.
I cannot find any documentation to support what we need here.
Is there a way for RestKit to do what we need?
If not, how do I get offline changes to persist to the disk (and not cache)? Then would it be appropriate to flag those as not uploaded to server, and then try uploading them when we are back online?
Any other important things I should consider?
At the time of writing RestKit does not support that feature.
To save to disk you need to call saveToPersistentStore: instead of just save: on the MOC.
You need to implement a scheme yourself, observing the 'online' status of the app and scanning the data store for things that need to be uploaded (which means maintaining a flag to indicate if it's happened yet).
I solved this issue by adding another field called 'updated' to my object. This field is set to true or 1 when the object is created or modified. Each time the application is started or synchronized, it iterates through the local core data copy and sends the objects with 'updated' set. On the web service, the response ALWAYS clears 'updated' to false when returning a response. This works well in the case where the web service and app are both online.
I’m developing a iOS App and I want to have a level of offline support and I’m struggling out of local datastore or cache which approach to use as It appears that you can’t use these two feature together.
My query is quite basic and doesn’t change only the data that is retrieved can change.
if i used one of the cache policies, i get connection errors and nothing appears to be returned from the cache.
The workflow i’m after is on the lines of below.
->When connected to the internet perform query and store objects locally.
->if there is no internet retrieve previously downloaded objects.
For the workflow you describe I think you're looking for a cache. If you would like the user could modify the data without connection and then, when there is wifi again, synchronise the local data with the remote data then you'll need the local datastore behavior.
The problem for me is when you want both in different parts of the same app because in parse in you use local datastore you can't use the cache. I don't really understand why!
I am using RestKit for an iOS To app. I already had done following using restkit:
1. Pull server objects from rest api in json format.
2. Delete orphan objects in core data which are no longer present on server.
Now i have to build the following scenario, if the internet is available on the device and user is adding a new data item,then what should i do first i.e should i store the new data first locally and then post to server or first i post the data to server and the pull it back on device ?
Secondly if the internet is not available on device and user inserts a new data item then saves data locally, On internet availability how do i post newly added data items to the server i.e what approach should i follow and if restkit can help me tackling this scenario ?
RestKit includes reachability monitoring (actually part of AFNetworking). So you can set a block to be run when the status changes:
[objectManager.HTTPClient setReachabilityStatusChangeBlock:...
Generally, store the item locally in all cases. When the item has been pushed to the server, set the sync date or a flag on the item to confirm that it has been updated.
This is really a broader question about how you manage local modifications and updates to the server. You may want an overall scheme to list the dirty objects and push updates to the server and have the server response set the sync time for each item. If you use 2 dates (one for the last local modification and one for the remote sync) then a quick predicate fetch on the model will tell you which objects are dirty and need to be pushed to the server.
I'm developing a blackberry application to remotely access an external customer database.
Selected employees can change customer entries via a webinterface accessible in our intranet.
I don't want the blackberry to contact the database on every request, so I built in a local storage, which stores the top 50 selected customers of the blackberry user.
What the best practice to keep both records in sync? I thought about creating an hashcode of each record to reduce the datasize to transfer (and though the energy necessary to transmit it). Can anyone here tell me what they do, to reduce requests by a mobile device?
Thanks,
rAyt
In a couple of different situations I've added a created/modified timestamp to each record. On a successful sync with the server, you note the last server time, store it on the client, and on the next sync only get the records (if any) that have changed since the last one. This will reduce data but you may still have to deal with records that were changed on both client and server since the last sync.