RestKit custom RKValueTransformer not being run for NSDate property - ios

Question

I would like to run a custom RKValueTransformer on an NSDate property when creating a specific request. I'm happy (and would prefer to) use the default in all other scenarios. My understanding is that I can set up the mapping, specify a value transformer and it'll use that, only falling back to the defaults if no value transformer is set. I'm running RestKit 0.23.3.
I have the following mapping set up for my request (I've obviously trimmed a bunch from this):
#property (nonatomic, retain) NSDate * dueDate;
...
+(RKEntityMapping *) createRequestMapping
{
static RKEntityMapping* map = nil;
if (map == nil)
{
map = (RKEntityMapping *)[RKObjectMapping requestMapping];
[map addAttributeMappingsFromDictionary:...];
RKValueTransformer *dueDateValueTransformer = [RKBlockValueTransformer valueTransformerWithValidationBlock:^BOOL(__unsafe_unretained Class inputValueClass, __unsafe_unretained Class outputValueClass) {
return [inputValueClass isSubclassOfClass:[NSDate class]];
} transformationBlock:^BOOL(id inputValue, __autoreleasing id *outputValue, __unsafe_unretained Class outputClass, NSError *__autoreleasing *error) {
*outputValue = [[self dueDateRequestFormatter] stringFromDate:inputValue];
return YES;
}];
RKAttributeMapping *dueDateMapping = [RKAttributeMapping attributeMappingFromKeyPath:#"dueDate" toKeyPath:#"due_date"];
dueDateMapping.valueTransformer = dueDateValueTransformer;
[map addPropertyMapping:dueDateMapping];
}
return map;
}
When my test for this runs, I can see that the mapping is used (since the target key path "due_date" exists in the dictionary), but the value transformer is not - rather, it appears the default NSDate transformer is used:
XCTAssertEqualObjects(#"2014-05-01", [item objectForKey:#"due_date"]);
-[RestKitCreateMappingTests testCreateSequenceMappings] failed: ((#"2014-05-01") equal to ([item objectForKey:#"due_date"])) failed: ("2014-05-01") is not equal to ("2014-05-01 00:00:00 +0000")
I've set breakpoints in both the validation and transformation blocks, and neither is hit.
Why is RestKit not using my value transformer?

Answer 1

I had to specify the propertyValueClass so that RestKit knew what type of target property to map to:
RKAttributeMapping *dueDateMapping = [RKAttributeMapping attributeMappingFromKeyPath:#"dueDate" toKeyPath:#"due_date"];
dueDateMapping.valueTransformer = dueDateValueTransformer;
dueDateMapping.propertyValueClass = [NSString class];
[map addPropertyMapping:dueDateMapping];
Without this, the following check failed in the mapping operation, and it never got a chance to use the custom value transformer, rather it just outputs the input value:
Class transformedValueClass = propertyMapping.propertyValueClass ?: [self.objectMapping classForKeyPath:propertyMapping.destinationKeyPath];
if (! transformedValueClass) {
*outputValue = inputValue;
return YES;
}
BOOL success = [propertyMapping.valueTransformer transformValue:inputValue toValue:outputValue ofClass:transformedValueClass error:error];
return success;