iPhone Core Data Lightweight Migration: Can't merge models

问题

I just started with iPhone core data and I ran into a problem in lightweight migration.

I added two new fields to my old model
Regenerated the model class files
Made the new model version as current version
Added the following code in AppDelegate in the template generated

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], NSMigratePersistentStoresAutomaticallyOption, [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

if (![persistentStoreCoordinator_ addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:options error:&error]) {
Then at last, I did a clean build before running the app.

I get the following error when the app crashes...

The operation couldn’t be completed. (Cocoa error 134140.)" UserInfo=0x622b350 {reason=Can't find or automatically infer mapping model for migration

Now to debug I added the following code...

    NSError *error = nil;
    NSDictionary *sourceMetadata = [NSPersistentStoreCoordinator metadataForPersistentStoreOfType:NSSQLiteStoreType URL:storeURL error:&error];

    if (!sourceMetadata) {
        NSLog(@"sourceMetadata is nil");
    } else {
        NSLog(@"sourceMetadata is %@", sourceMetadata);
    }

This displays the following result...

2011-01-20 18:18:41.018 MyApp[4438:207] sourceMetadata is {
    NSPersistenceFrameworkVersion = 248;
    NSStoreModelVersionHashes =     {
        Fugitive = <e33370b6 e7ca3101 f91d2595 1e8bfe01 3e7fb4de 6ef2a31d 9e50237b b313d390>;
    };
    NSStoreModelVersionHashesVersion = 3;
    NSStoreModelVersionIdentifiers =     (
    );
    NSStoreType = SQLite;
    NSStoreUUID = "E711F65F-3C5A-4889-872B-6541E4B2863A";
    "_NSAutoVacuumLevel" = 2;
}

I checked the app bundle > MyApp.momd > VersionInfo.plist file

its got the following contents...

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>NSManagedObjectModel_CurrentVersionName</key>
    <string>MyApp 2</string>
    <key>NSManagedObjectModel_VersionHashes</key>
    <dict>
        <key>MyApp</key>
        <dict>
            <key>Fugitive</key>
            <data>
            4zNwtufKMQH5HSWVHov+AT5/tN5u8qMdnlAje7MT05A=
            </data>
        </dict>
        <key>MyApp 2</key>
        <dict>
            <key>Fugitive</key>
            <data>
            N58Lf4BNpACzrsHAb1+BQImgjsBZ+u5G0wGUyt84+Ec=
            </data>
        </dict>
    </dict>
</dict>
</plist>

What am I missing here?

UPDATE: The problem turned out to be a default value attribute that I had missed in the model.

回答1:

You might try forcing Core Data to infer a mapping model:

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], NSInferMappingModelAutomaticallyOption, nil];

If the changes to your model were trivial, then Core Data may be able to infer a mapping model. If that fails, then you will probably need to create a mapping model (and revert to the options that you are currently using).

Mapping models are easy to create. Be mindful, though, if you change a data model then you will need to update the mapping, too.

You might want to check out this SO post.

来源：https://stackoverflow.com/questions/4745886/iphone-core-data-lightweight-migration-cant-merge-models

标签

iphone

core-data

core-data-migration

mapping-model