CODEWITHSUNDEEP
iossqlitecore-data
aprunedamtz
aprunedamtz

Reputation: 169

Is it possible to save a NSManagedObjectModel?

I have the following requirement: create and populate a SQLite database with data from a .xml file, this file can have a different structure any time so I cannot create the NSManagedObjectModel with Xcode, it must be at runtime. I've successfully created a NSManagedObjectModel programmatically, created the persistent store and populated the sqlite file with data from the .xml . However, the next time I use the app the persistent store is not compatible with the NSManagedObjectModel (I don't want to recreate the Model every time I run the app, just the first time). Is there any way to save the model I created programmatically and load it the next time it is needed? All I can see in the examples are models being loaded from the NSBundle.

Upvotes: 0

Views: 605

Answers (2)

Tom Harrington
Tom Harrington

Reputation: 70956

Is there any way to save the model I created programmatically and load it the next time it is needed?

Yes. NSManagedObjectModel conforms to NSCoding, which means that you can easily convert it to/from NSData, and saving and reading NSData is easy.

To save a model:

NSString *modelPath = // path where you want to save
NSData *modelData = [NSKeyedArchiver archivedDataWithRootObject:self.managedObjectModel];
[modelData writeToFile:modelPath atomically:YES];

To read a saved model:

if ([[NSFileManager defaultManager] fileExistsAtPath:modelPath]) {
    NSData *savedModelData = [NSData dataWithContentsOfFile:modelPath];
    NSManagedObjectModel *savedModel = [NSKeyedUnarchiver unarchiveObjectWithData:savedModelData];
}

Upvotes: 5

Darrell
Darrell

Reputation: 95

I'm not sure if you are saying that the data in the xml file is changing each time or what. It sounds like you are referring to the data, not the data model. I can't answer specifically, but I would take the approach as follows.

If the data in the xml file is structured the same or close to the same each time, I would create a data model to match that.

Then I would write some sort of parser class that would read the xml and parse it into the Core Data data store according to you "ManagedObjectModel" or data model.

I have seen the error you are talking about when you change the datastore outside of Core Data. You need to let Core Data handle all the reading and writing to the data store or else Core Data will tell you basically that "Your Persistent Store was created or altered by something other than your ManagedObjectModel". I think this is what is happening.

I know I am not using the terminology exactly as Core Data puts it, but Core Data is confusing and I'm trying to convey the message and understanding.

I would also look in to using MagicalRecord. It Drastically makes Core Data easier to work with and there is a great tutorial on www.raywenderlich.com which you can find Here

I really hope this helps you out some. If not, please post some sample code or maybe an example of that xml you are referring to.

Good Luck

Upvotes: 0

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