ios - 没有找到适合核心数据迁移的映射模型

Question

我正在尝试执行需要 MappingModel 的 iOS 核心数据迁移。核心数据由于某种原因无法使用映射模型，它回退到自动轻量级迁移。

我启用了 MigrationDebug 选项以获取更多信息，但我看到的内容毫无意义。映射模型的源和目标散列与源和目标 ManagedObjectModel 相同，忽略顺序。似乎应该使用映射模型，但日志显示“找不到合适的映射模型”。

这是(省略的)日志:

CoreData: annotation: (migration)    will attempt automatic schema migration
CoreData: annotation: (migration) looking for mapping model with 
 source hashes: 
{
    TSBaseEntity = <4797118c 50068f2f f544d9a9 4884720b 55ec7e4d 0d4c8f4e 1ee44be3 b06d2edc>;
    TSBuyer = <91e837d1 3f348913 eff634d6 6fb9b3a6 747e2390 fbdc4ae6 32cc56d6 7582d4a8>;
    ...
}
 destination hashes: {
    TSBaseEntity = <4797118c 50068f2f f544d9a9 4884720b 55ec7e4d 0d4c8f4e 1ee44be3 b06d2edc>;
    TSBuyer = <e316a857 8919c4be eef15387 5c67a21b 67d32919 99ead438 1ff93c05 2e065fcc>;
    ...
}
CoreData: annotation: (migration) checking mapping model at path file://localhost/Users/xandrews/Library/Application%20Support/iPhone%20Simulator/6.1/Applications/0A84951E-21FC-47C0-A1B7-F880ACB672C4/Dev.app/Migrate_0_5_24To_0_5_27.cdm
 source hashes: 
{(
    <4797118c 50068f2f f544d9a9 4884720b 55ec7e4d 0d4c8f4e 1ee44be3 b06d2edc>,
    <91e837d1 3f348913 eff634d6 6fb9b3a6 747e2390 fbdc4ae6 32cc56d6 7582d4a8>,
    ...
)}
 destination hashes: {(
    <4797118c 50068f2f f544d9a9 4884720b 55ec7e4d 0d4c8f4e 1ee44be3 b06d2edc>,
    <e316a857 8919c4be eef15387 5c67a21b 67d32919 99ead438 1ff93c05 2e065fcc>,
    ...
)}
CoreData: annotation: (migration) no suitable mapping model found
CoreData: annotation: (migration) inferring a mapping model between data models with 
 source hashes: ...

Answer 1

Xcode 4 生成的映射模型不会生成迁移发生所需的正确哈希值。您可以使用以下代码将迁移日志的输出与映射文件的哈希值进行比较:

    NSString *mappingModelPath = [[NSBundle mainBundle] pathForResource:@"MappingFile" ofType:@"cdm"];
    NSMappingModel *mappingModel = [[NSMappingModel alloc] initWithContentsOfURL:[NSURL fileURLWithPath:mappingModelPath]];

    for (NSEntityMapping *entityMapping in mappingModel.entityMappings) {
        NSLog(@"%@: %@", entityMapping.sourceEntityName, entityMapping.sourceEntityVersionHash);
        NSLog(@"%@: %@", entityMapping.destinationEntityName, entityMapping.destinationEntityVersionHash);
    }

您会看到这些与迁移日志输出中的哈希值不匹配。

解决方法是在 Xcode 5 中生成映射文件。