add support to core data component to hook up relationships from foreign keys present in the server payload

Code/CoreData/RKManagedObject.h

@@ -105,6 +105,24 @@
  */
 + (id)objectWithPrimaryKeyValue:(id)value;
 
+/**
+ * Must return a dictionary mapping Core Data relationships for the managed object
+ * to their corresponding primary key properties on the managed object.  Must
+ * return an empty dictionary if there are no relationships to be mapped.
+ *
+ * For example, given a Project object associated with a user, where the user is
+ * specified by a userId property on the managed object:
+ *
+ * [NSDictionary dictionaryWithObject:@"userId" forKey:@"user"];
+ * Will hydrate the 'user' association on the managed object with the object
+ * in the local object graph having the primary key specified in the managed object's
+ * userId property.
+ * 
+ * In effect, this approach allows foreign key relationships between managed objects
+ * to be automatically maintained from the server to the underlying Core Data object graph.
+ */
++ (NSDictionary*)relationshipToPrimaryKeyPropertyMappings;
+
 /**
  * Returns the value of the primary key property for this object
  */

Code/CoreData/RKManagedObject.m

@@ -147,6 +147,10 @@
 	return [NSDictionary dictionary];
 }
 
++ (NSDictionary*)relationshipToPrimaryKeyPropertyMappings {
+	return [NSDictionary dictionary];
+}
+
 #pragma mark Helpers
 
 - (id)primaryKeyValue {

Code/CoreData/RKManagedObjectStore.h

@@ -7,6 +7,7 @@
 //
 
 #import <CoreData/CoreData.h>
+#import "RKManagedObject.h"
 #import "RKManagedObjectCache.h"
 
 /**
@@ -57,4 +58,13 @@ extern NSString* const RKManagedObjectStoreDidFailSaveNotification;
  */
 - (NSArray*)objectsWithIDs:(NSArray*)objectIDs;
 
+/**
+ * Retrieves a model object from the object store given the model object's class and
+ * the primaryKeyValue for the model object. This method leverages techniques specific to 
+ * Core Data for optimal performance. The return value will be nil in cases where an existing
+ * object cannot be found in the object store.
+ */
+- (RKManagedObject*)findInstanceOfManagedObject:(Class)class withPrimaryKeyValue:(id)primaryKeyValue;
+
+
 @end

Code/CoreData/RKManagedObjectStore.m

@@ -186,4 +186,31 @@ static NSString* const kRKManagedObjectContextKey = @"RKManagedObjectContext";
 	return objectArray;
 }
 
+- (RKManagedObject*)findInstanceOfManagedObject:(Class)class withPrimaryKeyValue:(id)primaryKeyValue {
+	RKManagedObject* object = nil;
+	if ([class respondsToSelector:@selector(allObjects)]) {
+		NSArray* objects = nil;
+		NSMutableDictionary* threadDictionary = [[NSThread currentThread] threadDictionary];
+		
+		if (nil == [threadDictionary objectForKey:class]) {
+			NSFetchRequest* fetchRequest = [class fetchRequest];
+			[fetchRequest setReturnsObjectsAsFaults:NO];			
+			objects = [class objectsWithFetchRequest:fetchRequest];
+			NSLog(@"Cacheing all %d %@ objects to thread local storage", [objects count], class);
+			NSMutableDictionary* dictionary = [NSMutableDictionary dictionary];
+			NSString* primaryKey = [class performSelector:@selector(primaryKeyProperty)];
+			for (id theObject in objects) {			
+				id primaryKeyValue = [theObject valueForKey:primaryKey];
+				[dictionary setObject:theObject forKey:primaryKeyValue];
+			}
+			
+			[threadDictionary setObject:dictionary forKey:class];
+		}
+		
+		NSMutableDictionary* dictionary = [threadDictionary objectForKey:class];
+		object = [dictionary objectForKey:primaryKeyValue];
+	}
+	return object;
+}
+
 @end

Code/ObjectMapping/RKObjectMapper.m

@@ -240,36 +240,13 @@ static const NSString* kRKModelMapperMappingFormatParserKey = @"RKMappingFormatP
 // Persistent Instance Finders
 
 - (id)findOrCreateInstanceOfModelClass:(Class)class fromElements:(NSDictionary*)elements {
-	NSArray* objects = nil;
 	id object = nil;
-	
-	// TODO: Core Data dependency... Push into objectStore
-	if ([class respondsToSelector:@selector(allObjects)]) {
-		NSMutableDictionary* threadDictionary = [[NSThread currentThread] threadDictionary];
-		
-		if (nil == [threadDictionary objectForKey:class]) {
-			NSFetchRequest* fetchRequest = [class fetchRequest];
-			[fetchRequest setReturnsObjectsAsFaults:NO];			
-			objects = [class objectsWithFetchRequest:fetchRequest];
-			NSLog(@"Cacheing all %d %@ objects to thread local storage", [objects count], class);
-			NSMutableDictionary* dictionary = [NSMutableDictionary dictionary];
-			NSString* primaryKey = [class performSelector:@selector(primaryKeyProperty)];
-			for (id theObject in objects) {			
-				id primaryKeyValue = [theObject valueForKey:primaryKey];
-				[dictionary setObject:theObject forKey:primaryKeyValue];
-			}
-			
-			[threadDictionary setObject:dictionary forKey:class];
-		}
-		
-		NSMutableDictionary* dictionary = [threadDictionary objectForKey:class];
-		if ([class respondsToSelector:@selector(objectWithPrimaryKeyValue:)]) {
-			NSString* primaryKeyElement = [class performSelector:@selector(primaryKeyElement)];
-			id primaryKeyValue = [elements objectForKey:primaryKeyElement];
-			object = [dictionary objectForKey:primaryKeyValue];
-		}
+	if ([class respondsToSelector:@selector(primaryKeyElement)]) {
+		NSString* primaryKeyElement = [class performSelector:@selector(primaryKeyElement)];
+		id primaryKeyValue = [elements objectForKey:primaryKeyElement];
+		object = [[[RKObjectManager sharedManager] objectStore] findInstanceOfManagedObject:class
+																		   withPrimaryKeyValue:primaryKeyValue];
 	}
-	
 	// instantiate if object is nil
 	if (object == nil) {
 		if ([class respondsToSelector:@selector(object)]) {
@@ -392,6 +369,30 @@ static const NSString* kRKModelMapperMappingFormatParserKey = @"RKMappingFormatP
 			[object setValue:child forKey:propertyName];
 		}
 	}
+	
+	if ([object isKindOfClass:[RKManagedObject class]]) {
+		RKManagedObject* managedObject = (RKManagedObject*)object;
+		NSDictionary* relationshipToPkPropertyMappings = [[managedObject class] relationshipToPrimaryKeyPropertyMappings];
+		for (NSString* relationship in relationshipToPkPropertyMappings) {
+			NSString* primaryKeyPropertyString = [relationshipToPkPropertyMappings objectForKey:relationship];
+			
+			NSNumber* objectPrimaryKeyValue = nil;
+			@try {
+				objectPrimaryKeyValue = [managedObject valueForKeyPath:primaryKeyPropertyString];
+			} @catch (NSException* e) {
+				NSLog(@"Caught exception:%@ when trying valueForKeyPath with path:%@ for object:%@", e, primaryKeyPropertyString, managedObject);
+			}
+			
+			NSDictionary* relationshipsByName = [[managedObject entity] relationshipsByName];
+			NSEntityDescription* relationshipDestinationEntity = [[relationshipsByName objectForKey:relationship] destinationEntity];
+			id relationshipDestinationClass = objc_getClass([[relationshipDestinationEntity managedObjectClassName] cStringUsingEncoding:NSUTF8StringEncoding]);
+			RKManagedObject* relationshipValue = [[[RKObjectManager sharedManager] objectStore] findInstanceOfManagedObject:relationshipDestinationClass
+																											   withPrimaryKeyValue:objectPrimaryKeyValue];			
+			if (relationshipValue) {
+				[managedObject setValue:relationshipValue forKey:relationship];
+			}
+		}
+	}
 }
 
 - (void)updateModel:(id)model fromElements:(NSDictionary*)elements {