ios - CoreData 自定义 NSMappingModel 不迁移数据

Question

我正在尝试使用 xcode (.xcdatamodel) 创建的数据模型和运行时以编程方式创建的映射模型手动调用 CoreData 迁移。 迁移似乎已完成且没有错误，但新创建的数据库中没有数据。数据库的结构在那里(表、Z_METADATA 等)，但数据没有结转，显然我的 NSMappingModel 没有被应用。

迁移总结:Country 实体已重命名为 Country2，Country.name 已重命名为 Country2.new_name。

NSMutableArray *attrMaps = [[NSMutableArray alloc] init];
NSPropertyMapping *pMap = [[NSPropertyMapping alloc] init];
pMap.name = @"new_name";
pMap.valueExpression = [NSExpression expressionForKeyPath:@"source.name"];
[attrMaps addObject:pMap];

NSEntityMapping *eMap = [[NSEntityMapping alloc] init];
eMap.sourceEntityName = @"Country";
eMap.destinationEntityName = @"Country2";
eMap.name = @"CountryToCountry2";
eMap.mappingType = NSTransformEntityMappingType;
eMap.attributeMappings = attrMaps;

NSMutableArray *eMaps = [[NSMutableArray alloc] init];
[eMaps addObject:eMap];

NSMappingModel *mappingModel = [[NSMappingModel alloc] init];
mappingModel.entityMappings = eMaps;

NSURL * storeURL = [NSURL URLWithString:[NSString stringWithFormat:@"file://%@/Documents/%@",NSHomeDirectory(),@"TestCoreData.sqlite"]];
NSURL * storeURL2 = [NSURL URLWithString:[NSString stringWithFormat:@"file://%@/Documents/%@",NSHomeDirectory(),@"TestCoreData2.sqlite"]];
NSMigrationManager *migman = [self getMigrationManager];

NSError * err;
BOOL ok = [migman migrateStoreFromURL:storeURL
                                 type:NSSQLiteStoreType
                              options:nil
                     withMappingModel:mappingModel
                     toDestinationURL:storeURL2
                      destinationType:NSSQLiteStoreType
                   destinationOptions:nil
                                error:&err];

更多信息

将我手工制作的 NSMappingModel 与在 XCode 的 GUI 中创建的模型进行比较，您可以看到一些差异:

来自 Xcode 的 GUI

 entityMappings (
"(NSEntityMapping), 
    name CountryToCountry2, 
    mappingType 5, 
    sourceEntityName Country, 
    sourceEntityVersionHash <828c33cf 3ffdc5df dd1e73e8 4f7b60a5 f10dcb43 af26adeb 33d2c518 0c992dd8>, 
    destinationEntityName Country2, 
    destinationEntityVersionHash <8cdb8ecf cb47b39d 4b45858f a247487a dd88088b f509a6ec cc938740 5cf7a041>, attributeMappings (
    "(NSPropertyMapping), name new_name, valueExpression $source.name, userInfo (null)"
    ), relationshipMappings (
), sourceExpression FETCH(FUNCTION($manager, "fetchRequestForSourceEntityNamed:predicateString:" , "Country", "TRUEPREDICATE"), $manager.sourceContext, NO),
   entityMigrationPolicyClassName (null), userInfo (null)"

我的

entityMappings (
"(NSEntityMapping), 
    name CountryToCountry2, 
    mappingType 5, 
    sourceEntityName Country, 
    sourceEntityVersionHash (null), 
    destinationEntityName Country2, 
    destinationEntityVersionHash (null), 
    attributeMappings (
    "(NSPropertyMapping), name new_name, valueExpression source.name, userInfo (null)",
    ), relationshipMappings (
), sourceExpression (null), 
   entityMigrationPolicyClassName (null), userInfo (null)"

更新

我已将此 sourceExpression 添加到我的实体映射中，现在 Country 的行已复制到新数据库，但它们是空的。所以 NSPropertyMappings 似乎仍然没有生效:

eMap.sourceExpression = [NSExpression expressionWithFormat:@"FETCH(FUNCTION($manager, \"fetchRequestForSourceEntityNamed:predicateString:\" , \"Country\", \"TRUEPREDICATE\"), $manager.sourceContext, NO)"];

Answer 1

NSPropertyMapping 的 valueExpression 定义不正确。它应该是 expressionWithFormat: 而不是 expressionForKeyPath: 和 $source 而不是 source。像这样:

pMap.valueExpression = [NSExpression expressionWithFormat:@"$source.name"];

这样，我就有了一个实际工作的手工制作的 NSMappingModel。