Question

我有以下JSON：

{
    "users": [
        {"id": "1", "name": "John Doe"},
        {"id": "2", "name": "Bill Nye"}
    ],
    "groups": [
        {"id": "1", "name": "Group1", "users": ["1", "2"]},
        {"id": "2", "name": "Group2", "users": ["1"]}
    ]
}

...以及包含User和Group对象的Core Data模型。组对象与用户具有多对多关系（NSSet）。

我发现以下线程似乎表明这是可能的，但没有解释如何执行这样的映射：

https://github.com/RestKit/RestKit/issues/284

如何执行此映射，以便每个组的“用户”关系正确连接？

注意：我设置了映射，可以将JSON用户和组正确映射到各自的Core Data对象。但是，每个组的“用户”NSSet都是空的。

Answer 1

所以，我用RestKit 0.20（pre2）来计算它。

需要将JSON更改为以下内容（请注意组的users数组中的属性名称）：

{
    "users": [
        {"id": "1", "name": "John Doe"},
        {"id": "2", "name": "Bill Nye"}
    ],
    "groups": [
        {"id": "1", "name": "Group1", "users": [{"id" : "1"}, {"id" : "2"}]},
        {"id": "2", "name": "Group2", "users": [{"id" : "1"}]}
    ]
}

然后，以下映射：

RKEntityMapping *userMapping = [RKEntityMapping mappingForEntityForName:@"User" inManagedObjectStore:managedObjectStore];
userMapping.identificationAttributes = @[@"id"];
[userMapping addAttributeMappingsFromArray:@[@"id", @"name"]];
RKEntityMapping *groupMapping = [RKEntityMapping mappingForEntityForName:@"Group" inManagedObjectStore:managedObjectStore];
groupMapping.identificationAttributes = @[@"id"];
[groupMapping addAttributeMappingsFromArray:@[@"id", @"name"]];
[groupMapping addRelationshipMappingWithSourceKeyPath:@"users" mapping:userMapping];

最后，以下responseDescriptors：

RKResponseDescriptor *userResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:classMapping pathPattern:@"/api/allthejson" keyPath:@"users" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
RKResponseDescriptor *groupResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:classMapping pathPattern:@"/api/allthejson" keyPath:@"groups" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];
[objectManager addResponseDescriptorsArray:@[userResponseDescriptor, groupResponseDescriptor]];

然后使用RKObjectManager的getObjectsAtPath获取对象：参数：success：failure方法和你的完成！

Answer 2

RestKit存在许多问题，特别是在建模关系方面。调试映射可能令人生畏。

以下是一些代码，用于处理您在没有RestKit的情况下所描述的内容。

NSArray *userArray; 
// an array populated with NSManagedObjects 
// correctly converted from JSON to the User entity

NSArray *groups = [jsonObject objectForKey:@"groups"];

for (NSDictionary *d in groups) {
   Group *g = [NSEntityDescription insertNewObjectForEntityForName:@"Group"
                  inManagedObjectContext:_managedObjectContext];
   g.id = @([d[@"id"] intValue]);
   g.name = d[@"name"];
   NSArray *users = d[@"users"];
   for (NSString *s in users) {
      User *u = [[userArray filteredArrayUsingPredicate:
        [NSPredicate predicateWithFormat:@"id = %@", @([s intValue])]]
          objectAtIndex:0];
      [g addUsersObject:u];
   }
}
// save

RestKit - Hydrate数组外键

2 个答案: