RestKit Identical To-One Mappings on Separate Objects Excepts - objective-c

Question

I know what I'm doing is quite simple, and I'm a bit confused as to what I'm doing wrong here.
I'm trying to have a given key on a JSON object always map to the same Objective-C class. This key has the same name on all of the JSON object's that have it (device).
I have two classes, Foo and Bar that each have a device property:
#interface Foo
#property (strong, nonatomic) Device * device;
#end
#interface Bar
#property (strong, nonatomic) Device * device;
#end
#interface Device
#property (strong, nonatomic) NSString * deviceId;
#property (strong, nonatomic) NSString * deviceName;
#end
And for the JSON that's sent by my server for Foo and Bar, the device is represented like so:
{
"device": {
"deviceId": "someId",
"deviceName": "someName"
}
}
In a configuration function for RestKit in my application, I have the following:
RKObjectMapping * responseMapping = [RKObjectMapping mappingForClass: model[#"class"]];
if ( model[#"class"] == [Foo class] ||
model[#"class"] == [Bar class] ){
NSArray * defaultRequestKeys = #[#"id", #"createdAt", #"updatedAt"];
NSArray * defaultModelKeys = #[#"objectId", #"createdAt", #"updatedAt"];
NSArray * deviceRequestKeys = [#[#"deviceName", #"deviceId"] arrayByAddingObjectsFromArray: defaultRequestKeys];
NSArray * deviceModelKeys = [#[#"deviceName", #"deviceId"] arrayByAddingObjectsFromArray: defaultModelKeys];
RKObjectMapping * deviceResponseMapping;
deviceResponseMapping = [RKObjectMapping mappingForClass: [Device class]];
[deviceResponseMapping addAttributeMappingsFromDictionary: [NSDictionary dictionaryWithObjects: deviceModelKeys
forKeys: deviceRequestKeys]];
[responseMapping addRelationshipMappingWithSourceKeyPath:#"device" mapping: deviceResponseMapping];
}
However, RestKit excepts with failed: caught "NSInternalInconsistencyException", "Unable to add mapping for keyPath device, one already exists..."
Which means I'm doing something wrong.
I've tried looking all through the docs and I'm confused how I have the same key on two different objects use the same object mapping. This is for the Device to-one relationship on Foo and Bar.

Answer 1

In my case, I had declared this key already outside of the call to
[responseMapping addRelationshipMappingWithSourceKeyPath:#"device" mapping: deviceResponseMapping];
In another part of the code. Removing this key fixed the problem. I was adding it with:
[responseMapping addAttributeMappingsFromDictionary: responseAttributeMappings];