RestKit: How does one post an array of objects?

问题:

Question summary:

Consider a class SyncObject that is KVC-compliant with properties such as: time, someValue, lastChange, uuid.

Consider an NSArray containing exclusively instances of SyncObject.

I need to submit the array to the server as a JSON array.

How would one submit this array to the server using HTTP POST using RestKit?

Example array:

[
  {
    "time": "14:45 10/21/2011",
    "someValue": "15",
    "lastChange": "14:45 10/21/2011",
    "uuid": "0b07c510-f4c8-11e0-be50-0800200c9a66"
  },
  {
    "time": "14:50 10/21/2011",
    "someValue": "62",
    "lastChange": "14:51 10/21/2011",
    "uuid": "1a6d4480-f4c8-11e0-be50-0800200c9a66"
  }
]

---

Details

I have an array of objects that I need to the server as JSON. It seems to me that RestKit is the easiest way to do this: I'm trying to avoid converting objects into a set of NSDictionary objects, and then using some JSON encoder to get JSON which I can POST to the server.

So, having created the array, and having set up the mapping for the class of objects stored in the array, I naturally try to POST to the server.

RKObjectManager* mgr = [RKObjectManager objectManagerWithBaseURL:@"http://localhost/someweb/api/"];
mgr.serializationMIMEType = RKMIMETypeFormURLEncoded;
mgr.client.username = @"username";
mgr.client.password = @"password";
RKObjectMapping* mapping = [RKObjectMapping mappingForClass:[NSMutableDictionary class]];
[mapping mapKeyPath: @"time"       toAttribute:@"time"         ];  
[mapping mapKeyPath: @"someValue"  toAttribute:@"someValue"    ];
[mapping mapKeyPath: @"lastChange" toAttribute:@"lastChange"   ];
[mapping mapKeyPath: @"uuid"       toAttribute:@"uuid"         ];
RKObjectMapping* mappingForSerialization = [mapping inverseMapping];
[mgr.mappingProvider setSerializationMapping:mappingForSerialization 
                                    forClass:[NSManagedObject class]];

[mgr.router routeClass:[NSManagedObject class] toResourcePath:@"/sync" forMethod:RKRequestMethodPOST];    

[mgr postObject:array delegate:nil/*self*/];

However, this is what I get out:

2011-10-11 14:57:51.769 AppConnect[1974:6e0b] *** Terminating app due to uncaught exception '(null)', reason: 'Unable to find a routable path for object of type '__NSArrayI' for HTTP Method 'POST''

Apparently, RestKit does not know how to handle NSArrays.

How does one post an array of objects using RestKit?

---

I've tried something different: I replaced the last line with a manual send through RKObjectLoader.

//[mgr postObject:[NSMutableDictionary dictionaryWithObject:array forKey:@"data"] delegate:nil/*self*/];


NSString* syncPath = @"/sync"; 
RKObjectLoader * objectLoader = [mgr objectLoaderWithResourcePath:syncPath delegate:self];
objectLoader.serializationMIMEType = RKMIMETypeJSON;
objectLoader.method = RKRequestMethodPOST;
//objectLoader.objectClass = [NSManagedObject class];       
//objectLoader.managedObjectStore = mgr.objectStore; 
objectLoader.params = [NSDictionary dictionaryWithObject:array 
                                                  forKey:@"MyData"]; 
[objectLoader send];

Unfortunately, this does not apply mapping of any sort, and instead transmits an array of objects' descriptions. Setting serializationMIMEType also does not affect the structure of transmitted contents, and params are always transmitted as application/x-www-form-urlencoded.

I also tried assigning serialization mapping and passing the object as targetObject and sourceObject (this seems to be what RestKit does internally in -[RKObjectManager postObject:delegate:]).

RKObjectLoader * objectLoader = [mgr objectLoaderWithResourcePath:syncPath delegate:self];
objectLoader.method = RKRequestMethodPOST;
//objectLoader.objectClass = [NSManagedObject class];       
//objectLoader.managedObjectStore = mgr.objectStore; 
objectLoader.params = [NSMutableDictionary dictionaryWithObject:array 
                                                  forKey:@"MyData"]; 
objectLoader.serializationMapping = mapping;
objectLoader.serializationMIMEType = RKMIMETypeJSON;
objectLoader.sourceObject = objectLoader.params;
objectLoader.targetObject = objectLoader.params;
[objectLoader send];

Unfortunately, no mapping occurs this way:

2011-10-12 12:36:48.143 MyProject[5119:207] D restkit.network:RKObjectLoader.m:290 POST or PUT request for source object {
    MyData =     (
        "<NSManagedObject: 0x5935430> (entity: SomeRecord; id: 0x5934da0 <x-coredata://64DF9977-DA50-4FCD-8C20-4132E58439BF/SomeRecord/p1> ; data: <fault>)",
        "<NSManagedObject: 0x5935730> (entity: SomeRecord; id: 0x5934db0 <x-coredata://64DF9977-DA50-4FCD-8C20-4132E58439BF/SomeRecord/p2> ; data: <fault>)"
    );
}, serializing to MIME Type application/json for transport...
2011-10-12 12:36:48.143 MyProject[5119:207] D restkit.object_mapping:RKObjectMappingOperation.m:428 Starting mapping operation...
2011-10-12 12:36:48.145 MyProject[5119:207] T restkit.object_mapping:RKObjectMappingOperation.m:291 Did not find mappable attribute value keyPath 'time'
2011-10-12 12:36:48.145 MyProject[5119:207] T restkit.object_mapping:RKObjectMappingOperation.m:291 Did not find mappable attribute value keyPath 'someValue'
2011-10-12 12:36:48.145 MyProject[5119:207] T restkit.object_mapping:RKObjectMappingOperation.m:291 Did not find mappable attribute value keyPath 'lastChange'
2011-10-12 12:36:48.145 MyProject[5119:207] T restkit.object_mapping:RKObjectMappingOperation.m:291 Did not find mappable attribute value keyPath 'uuid'
2011-10-12 12:36:48.145 MyProject[5119:207] D restkit.object_mapping:RKObjectMappingOperation.m:448 Mapping operation did not find any mappable content
2011-10-12 12:36:48.146 MyProject[5119:207] T restkit.network:RKRequest.m:211 Prepared POST URLRequest '<NSMutableURLRequest http://someurl/api/sync?request=provide_key>'. HTTP Headers: {
    Accept = "application/json";
    "Content-Length" = 0;
}. HTTP Body: .

回答1:

The restkit does not fund routable path for NSArray, because you defined your routing for NSManagedObject class. You probably want to create a custom class, say MySyncEntity that holds the ivars you define in your mapping. Then, you create your mapping like this:

RKObjectMapping* mapping = [RKObjectMapping mappingForClass:[MySyncEntity class]];
....
[myManager setSerializationMIMEType:RKMIMETypeJSON];
[[myManager router] routeClass:[MySyncEntity class] toResourcePath:@"/sync"];

then you should be able to post your object to the API backend as JSON object.

Further clarification:

In this case, we want to post an array of NSManagedObject instances into a JSON based API. To do that we need to create a sync entity, that holds the objects in an array:

@interface MySyncEntity : NSObject {}
@property (nonatomic, retain) NSArray* mySyncArray;
...
@end 

The mySyncArray will hold the payload we'd like to submit to the rest backend. Then, we create appropriate mapping for both NSManagedObject that will be sent in mySyncArray and the MySyncEntity entity itself.

RKObjectManager *manager = [RKObjectManager objectManagerWithBaseURL:kBaseUrl];
...
RKObjectMapping *mngObjMapping = [RKObjectMapping mappingForClass:[NSManagedObject class]]; 
[mngObjMapping mapKeyPath: @"time" toAttribute:@"time"];  
[mngObjMapping mapKeyPath: @"recordLevel" toAttribute:@"recordLevel"];
.... //map as many properties as you wish
[[manager mappingProvider] setSerializationMapping:[mngObjMapping inverseMapping]
                                          forClass:[NSManagedObject class]];

//now, we create mapping for the MySyncEntity
RKObjectMapping *syncEntityMapping = [RKObjectMapping mappingForClass:[MySyncEntity class]];
[syncEntityMapping mapKeyPath:@"mySyncArray" toRelationship:@"mySyncArray" withMapping:mngObjMapping];
[[manager mappingProvider] setSerializationMapping:[syncEntityMapping inverseMapping]
                                          forClass:[MySyncEntity class]];

Now with the mappings defined we can post the object to the server

[manager postObject:mySyncInstance delegate:nil];

The contents of mySyncInstance array will be mapped according to mngObjMapping and sent to defined rest endpoint.

回答2:

As a further clarification, I'd like to point out that in mja's answer the key thing is

[syncEntityMapping mapKeyPath:@"mySyncArray" toRelationship:@"mySyncArray" withMapping:mngObjMapping];

This says "the mySyncArray keypath is an array which contains objects that should be mapped according to mngObjMapping".