Add assertions to prevent attempts to create request descriptor objects with inappropriate mappings. fixes #976

Code/Network/RKRequestDescriptor.m

@@ -22,6 +22,25 @@
 //
 
 #import "RKRequestDescriptor.h"
+#import "RKObjectMapping.h"
+#import "RKDynamicMapping.h"
+
+static void RKAssertValidMappingForRequestDescriptor(RKMapping *mapping)
+{
+    if ([mapping isKindOfClass:[RKObjectMapping class]]) {
+        if (! [[(RKObjectMapping *)mapping objectClass] isEqual:[NSMutableDictionary class]]) {
+            [NSException raise:NSInvalidArgumentException format:@"`RKRequestDescriptor` objects must be initialized with a mapping whose target class is `NSMutableDictionary`, got '%@' (see `[RKObjectMapping requestMapping]`)", [(RKObjectMapping *)mapping objectClass]];
+        }
+    } else if ([mapping isKindOfClass:[RKDynamicMapping class]]) {
+        [[(RKDynamicMapping *)mapping objectMappings] enumerateObjectsUsingBlock:^(RKObjectMapping *objectMapping, NSUInteger idx, BOOL *stop) {
+            if (! [objectMapping.objectClass isEqual:[NSMutableDictionary class]]) {
+                [NSException raise:NSInvalidArgumentException format:@"`RKRequestDescriptor` objects may only be initialized with `RKDynamicMapping` objects containing `RKObjectMapping` objects whose target class is `NSMutableDictionary`, got '%@' (see `[RKObjectMapping requestMapping]`)", objectMapping.objectClass];
+            }
+        }];
+    } else {
+        [NSException raise:NSInvalidArgumentException format:@"Expected an instance of `RKObjectMapping` or `RKDynamicMapping`, instead got '%@'", [mapping class]];
+    }
+}
 
 @interface RKRequestDescriptor ()
 
@@ -37,6 +56,7 @@
 {
     NSParameterAssert(mapping);
     NSParameterAssert(objectClass);
+    RKAssertValidMappingForRequestDescriptor(mapping);
 
     RKRequestDescriptor *requestDescriptor = [self new];
     requestDescriptor.mapping = mapping;

Code/ObjectMapping/RKDynamicMapping.h

@@ -55,6 +55,13 @@ typedef RKObjectMapping *(^RKDynamicMappingDelegateBlock)(id);
  */
 - (void)setObjectMapping:(RKObjectMapping *)objectMapping whenValueOfKeyPath:(NSString *)keyPath isEqualTo:(id)value;
 
+/**
+ Returns an array of object mappings that have been registered with the receiver.
+ 
+ @return An array of `RKObjectMapping` objects registered with the receiver.
+ */
+@property (nonatomic, readonly) NSArray *objectMappings;
+
 ///-----------------------------------------------------------------
 /// @name Retrieving the Object Mapping for an Object Representation
 ///-----------------------------------------------------------------

Code/ObjectMapping/RKDynamicMapping.m

@@ -43,6 +43,11 @@
     return self;
 }
 
+- (NSArray *)objectMappings
+{
+    return [self.matchers valueForKey:@"objectMapping"];
+}
+
 - (void)setObjectMapping:(RKObjectMapping *)objectMapping whenValueOfKeyPath:(NSString *)keyPath isEqualTo:(id)expectedValue
 {
     RKLogDebug(@"Adding dynamic object mapping for key '%@' with value '%@' to destination class: %@", keyPath, expectedValue, NSStringFromClass(objectMapping.objectClass));