Merge pull request #160 from github/nil-dictionary-error

JSON dictionary error handling redux

Mantle/MTLJSONAdapter.h

@@ -60,6 +60,9 @@ extern NSString * const MTLJSONAdapterErrorDomain;
 // +classForParsingJSONDictionary: returned nil for the given dictionary.
 extern const NSInteger MTLJSONAdapterErrorNoClassFound;
 
+// The provided JSONDictionary is not valid.
+extern const NSInteger MTLJSONAdapterErrorInvalidJSONDictionary;
+
 // Converts a MTLModel object to and from a JSON dictionary.
 @interface MTLJSONAdapter : NSObject
 
@@ -95,7 +98,8 @@ extern const NSInteger MTLJSONAdapterErrorNoClassFound;
 //
 // JSONDictionary - A dictionary representing JSON data. This should match the
 //                  format returned by NSJSONSerialization. If this argument is
-//                  nil, the method returns nil.
+//                  nil, the method returns nil and an error with code
+//                  MTLJSONAdapterErrorInvalidJSONDictionary.
 // modelClass     - The MTLModel subclass to attempt to parse from the JSON.
 //                  This class must conform to <MTLJSONSerializing>. This
 //                  argument must not be nil.

Mantle/MTLJSONAdapter.m

@@ -12,6 +12,7 @@
 
 NSString * const MTLJSONAdapterErrorDomain = @"MTLJSONAdapterErrorDomain";
 const NSInteger MTLJSONAdapterErrorNoClassFound = 2;
+const NSInteger MTLJSONAdapterErrorInvalidJSONDictionary = 3;
 
 // An exception was thrown and caught.
 static const NSInteger MTLJSONAdapterErrorExceptionThrown = 1;
@@ -71,7 +72,17 @@ - (id)initWithJSONDictionary:(NSDictionary *)JSONDictionary modelClass:(Class)mo
 	NSParameterAssert([modelClass isSubclassOfClass:MTLModel.class]);
 	NSParameterAssert([modelClass conformsToProtocol:@protocol(MTLJSONSerializing)]);
 
-	if (JSONDictionary == nil) return nil;
+
+	if (JSONDictionary == nil) {
+		if (error != NULL) {
+			NSDictionary *userInfo = @{
+				NSLocalizedDescriptionKey: NSLocalizedString(@"Invalid JSONDictionary", @""),
+				NSLocalizedFailureReasonErrorKey: NSLocalizedString(@"The JSONDictionary parameter is invalid.", @"")
+			};
+			*error = [NSError errorWithDomain:MTLJSONAdapterErrorDomain code:MTLJSONAdapterErrorInvalidJSONDictionary userInfo:userInfo];
+		}
+		return nil;
+	}
 
 	if ([modelClass respondsToSelector:@selector(classForParsingJSONDictionary:)]) {
 		modelClass = [modelClass classForParsingJSONDictionary:JSONDictionary];

MantleTests/MTLJSONAdapterSpec.m

@@ -73,11 +73,13 @@
 	expect([MTLJSONAdapter JSONDictionaryFromModel:model]).to.equal(values);
 });
 
-it(@"should return nil with a nil JSON dictionary, but no error", ^{
+it(@"should return nil and an error with a nil JSON dictionary", ^{
 	NSError *error = nil;
 	MTLJSONAdapter *adapter = [[MTLJSONAdapter alloc] initWithJSONDictionary:nil modelClass:MTLTestModel.class error:&error];
 	expect(adapter).to.beNil();
-	expect(error).to.beNil();
+	expect(error).notTo.beNil();
+	expect(error.domain).to.equal(MTLJSONAdapterErrorDomain);
+	expect(error.code).to.equal(MTLJSONAdapterErrorInvalidJSONDictionary);
 });
 
 it(@"should ignore unrecognized JSON keys", ^{