Restkit property mapping Failed Transformation error

问题

this is what my sample code looks like:

{
    "name": "Ahmad Mansour",
    "subjects": [
        {
            "parent_subject_name": "Arabic",
            "subject_name": "Shafahi",
            "exams": [
                {
                    "score": "30.00",
                    "exam_name": "Sa3i 1 "
                },
                {
                    "score": "50.00",
                    "exam_name": "sa3i 2"
                },
                {
                    "score": "100.00",
                    "exam_name": "First Semester Exam"
                }
            ]
        },
        {
            "parent_subject_name": "Arabic",
            "subject_name": "Khati",
            "exams": [
                {
                    "score": "50.00",
                    "exam_name": "Sa3i 1 "
                },
                {
                    "score": "60.00",
                    "exam_name": "sa3i 2"
                },
                {
                    "score": "95.00",
                    "exam_name": "First Semester Exam"
                }
            ]
        },

for the subject entity.. my mapping works just fine:

RKEntityMapping *subjectEntityMapping = [RKEntityMapping mappingForEntityForName:kSubjectIdentity inManagedObjectStore:model.managedObjectStore];
[subjectEntityMapping addAttributeMappingsFromDictionary:@{ @"subject_name": @"name",
                                                            @"parent_subject_name" :@"parent_name"
                                                          }];

subjectEntityMapping.identificationAttributes = @[ @"name" ];

RKResponseDescriptor *studentResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:subjectEntityMapping pathPattern:kGradesPath keyPath:@"subjects" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];

[model.objectManager addResponseDescriptor:studentResponseDescriptor];

but when i do the exam score mapping.. things blow up:

RKEntityMapping *examEntityMapping = [RKEntityMapping mappingForEntityForName:kExamIdentity inManagedObjectStore:model.managedObjectStore];
[examEntityMapping addAttributeMappingsFromDictionary:@{ @"exams.exam_name": @"name" }];

examEntityMapping.identificationAttributes = @[ @"name" ];

RKResponseDescriptor *examResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:examEntityMapping pathPattern:kGradesPath keyPath:@"subjects" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];

[model.objectManager addResponseDescriptor:examResponseDescriptor];

i get the following error:

 E restkit.object_mapping:RKMappingOperation.m:431 Failed transformation of value at keyPath 'exams.exam_name' to representation of type 'NSString': Error Domain=org.restkit.RKValueTransformers.ErrorDomain Code=3002 "Failed transformation of value '(
    "Sa3i 1 ",
    "sa3i 2",
    "First Semester Exam"
)' to NSString: none of the 2 value transformers consulted were successful." UserInfo=0x9a508a0 {detailedErrors=(
    "Error Domain=org.restkit.RKValueTransformers.ErrorDomain Code=3002 \"The given value is not already an instance of 'NSString'\" UserInfo=0x9a50800 {NSLocalizedDescription=The given value is not already an instance of 'NSString'}",
    "Error Domain=org.restkit.RKValueTransformers.ErrorDomain Code=3000 \"Expected an `inputValue` of type `NSNull`, but got a `__NSArrayI`.\" UserInfo=0x9a50830 {NSLocalizedDescription=Expected an `inputValue` of type `NSNull`, but got a `__NSArrayI`.}"

I also tried this mapping, but i get the exact same error:

[examEntityMapping addAttributeMappingsFromDictionary:@{ @"exam_name": @"name" }];

examEntityMapping.identificationAttributes = @[ @"name" ];

RKResponseDescriptor *examResponseDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:examEntityMapping pathPattern:kGradesPath keyPath:@"subjects.exams" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassSuccessful)];

ideas?

回答1:

You shouldn't have a response descriptor for exams. It's nested data in your subject so it should be mapped using a relationship on the subject mapping.

Using the response descriptor doesn't work because you're trying to map into 2 arrays when the mapping only caters for one. Hence you get an error when RestKit tries to convert an array into a string.

Also, for your exam mapping you should probably specify multiple attributes for the unique identity as exam names are used repeatedly for different instances...

来源：https://stackoverflow.com/questions/19607672/restkit-property-mapping-failed-transformation-error