How do I map custom error keys in Restkit? - ios

Question

When a user signs up successfully on our server, it responds with a 200 status code and a JSON payload like this:
{
"error": null,
"result": {
"auth": {
"created_utc": 1420740197,
"device_token": "rQZJddrbD5tyEpznb8bVKeGlHqRNGyvOgDR;tQJBkpkfAXO6DQ4lNiG17lzu6IDc0hVBfR3RrN9o0txRQIYAa6fnf5d9LNaSRDMk9LrplgkITuMC37v;;;rvG35CJvV7dWZ5TQVYUWeHwAABvKvzTRpSDw5Qg9jQrmiUHLZptegFY=76421420740197"
},
"display_name": "a",
"email": "a#a.com",
"user_id": 7642,
"username": "a"
}
}
But if a#a.com tries to sign up again, it responds with a 400 status code and a JSON payload like this:
{
"error": {
"code": 805,
"message": "there is another user with that username"
},
"result": null
}
I tried mapping the error, so that when Restkit returns an error, I get the message as well as the code. These are the ways I tried to do that:
RKObjectMapping *errorMapping = [RKObjectMapping mappingForClass:[RKErrorMessage class]];
[errorMapping addPropertyMapping:[RKAttributeMapping attributeMappingFromKeyPath:#"error.message" toKeyPath:#"errorMessage"]];
RKResponseDescriptor *errorDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:errorMapping method:RKRequestMethodAny pathPattern:nil keyPath:nil statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassClientError)];
[self.objectManager addResponseDescriptor:errorDescriptor];
This one obviously only gets the message part of the error to return with this output:
Error Domain=org.restkit.RestKit.ErrorDomain Code=1004 "there is another user with that username" UserInfo=0x7feefcf8a730 {RKObjectMapperErrorObjectsKey=(
"there is another user with that username"
), NSLocalizedDescription=there is another user with that username}
So then I tried making a subclass of RKErrorMessage:
#import "RKErrorMessage.h"
#interface TAG_RKErrorMessage : RKErrorMessage
#property (strong, nonatomic) NSNumber *errorCode;
#end
And changed the mapping to this:
RKObjectMapping *errorMapping = [RKObjectMapping mappingForClass:[TAG_RKErrorMessage class]];
[errorMapping addPropertyMapping:[RKAttributeMapping attributeMappingFromKeyPath:#"error.message" toKeyPath:#"errorMessage"]];
[errorMapping addPropertyMapping:[RKAttributeMapping attributeMappingFromKeyPath:#"error.code" toKeyPath:#"errorCode"]];
and that resulted in the exact same output:
Error Domain=org.restkit.RestKit.ErrorDomain Code=1004 "there is another user with that username" UserInfo=0x7fa16c627ce0 {RKObjectMapperErrorObjectsKey=(
"there is another user with that username"
), NSLocalizedDescription=there is another user with that username}
So lastly I tried this mapping to at least try to get the dictionary show up as the RKObjectMapperErrorObjectsKey of the NSError's userInfo:
RKObjectMapping *errorMapping = [RKObjectMapping mappingForClass:[RKErrorMessage class]];
[errorMapping addPropertyMapping:[RKAttributeMapping attributeMappingFromKeyPath:#"error" toKeyPath:#"errorMessage"]];
And that resulted in this output:
Error Domain=org.restkit.RestKit.ErrorDomain Code=1004 "<null>" UserInfo=0x7ff8abe678e0 {RKObjectMapperErrorObjectsKey=(
(null)
), NSLocalizedDescription=<null>}
Now I'm stuck at this point. How can I map the keys of my server's error response so that I can get access to the code that is returned as well as the message as two separate values?

Answer 1

You've likely mapped your TAG_RKErrorMessage instance correctly. Have you attempted to extract it from the NSError you've been given? You can use the RKObjectMapperErrorObjectsKey as a key on the NSError's userInfo dictionary to get an array of all mapped error messages:
NSArray* objectMapperErrorObjectsArray = [error.userInfo objectForKey:RKObjectMapperErrorObjectsKey];
You can then loop through that array to check each error for conditions you want to respond to, for example, if you wanted to respond to a 403 response code with the error message "Invalid token", you could do:
NSArray* objectMapperErrorObjectsArray = [error.userInfo objectForKey:RKObjectMapperErrorObjectsKey];
for (RKErrorMessage* objectMapperErrorObject in objectMapperErrorObjectsArray)
{
if ([objectMapperErrorObject.errorMessage isEqual:#"Invalid token"])
{
if (operation.HTTPRequestOperation.response.statusCode == 403)
{
//Code to handle a 403 response status code when error message is "Invalid token".
}
}
}

Answer 2

Just a hint: if you want to use the built-in RKErrorMessage without creating any subclass, you can map all error JSON attributes to RKErrorMessage.userInfo in this way:
Objective-C:
RKObjectMapping *errorMapping = [RKObjectMapping mappingForClass:[RKErrorMessage class]];
[errorMapping addPropertyMapping:[RKAttributeMapping attributeMappingFromKeyPath:nil toKeyPath:#"userInfo"]];
RKResponseDescriptor *errorDescriptor = [RKResponseDescriptor responseDescriptorWithMapping:errorMapping method:RKRequestMethodAny pathPattern:nil keyPath:"error" statusCodes:RKStatusCodeIndexSetForClass(RKStatusCodeClassClientError)];
Swift:
let errorMapping = RKObjectMapping(forClass: RKErrorMessage.self);
errorMapping.addPropertyMapping(RKAttributeMapping(fromKeyPath: nil, toKeyPath: "userInfo"));
let errorResponseDescriptor = RKResponseDescriptor(
mapping: errorMapping,
method: RKRequestMethod.Any,
pathPattern: nil,
keyPath: "error",
statusCodes: RKStatusCodeIndexSetForClass(UInt(RKStatusCodeClassClientError)))
);