Major overhaul to the Core Data managed object identification and relationship connection support.

* Replaces primary key with `RKEntityIdentifier`
* Add support for use of compound keys for object identification
* Refactor `RKConnectionMapping` to `RKConnectionDescription` and add support for connecting with multiple attributes
* Clarify naming of representation key methods to better match naming conventions
* Add type transformation support for object identification
* Greatly expand test coverage for object identification
* Drop the `NSEntityDescription` category
* Simplify the `RKManagedObjectCaching` protocol
* Add compound key support to the Fetch Request and In Memory Cache implementations
* Replace Kiwi with Specta for tests where contexts are helpful for organization
* Rename `defaultValueForMissingAttribute` to `defaultValueForAttribute`

Code/CoreData/RKConnectionDescription.m

@@ -0,0 +1,129 @@
+//
+//  RKConnectionDescription.m
+//  RestKit
+//
+//  Created by Blake Watters on 11/20/12.
+//  Copyright (c) 2012 RestKit. All rights reserved.
+//
+
+#import "RKConnectionDescription.h"
+
+static NSSet *RKSetWithInvalidAttributesForEntity(NSArray *attributes, NSEntityDescription *entity)
+{
+    NSMutableSet *attributesSet = [NSMutableSet setWithArray:attributes];
+    NSSet *validAttributeNames = [NSSet setWithArray:[[entity attributesByName] allKeys]];
+    [attributesSet minusSet:validAttributeNames];
+    return attributesSet;
+}
+
+// Provides support for connecting a relationship by
+@interface RKForeignKeyConnectionDescription : RKConnectionDescription
+@end
+
+// Provides support for connecting a relationship by traversing the object graph
+@interface RKKeyPathConnectionDescription : RKConnectionDescription
+@end
+
+@interface RKConnectionDescription ()
+@property (nonatomic, strong, readwrite) NSRelationshipDescription *relationship;
+@property (nonatomic, copy, readwrite) NSDictionary *attributes;
+@property (nonatomic, copy, readwrite) NSString *keyPath;
+@end
+
+@implementation RKConnectionDescription
+
+- (id)initWithRelationship:(NSRelationshipDescription *)relationship attributes:(NSDictionary *)attributes
+{
+    NSParameterAssert(relationship);
+    NSParameterAssert(attributes);
+    NSAssert([attributes count], @"Cannot connect a relationship without at least one pair of attributes describing the connection");
+    NSSet *invalidSourceAttributes = RKSetWithInvalidAttributesForEntity([attributes allKeys], [relationship entity]);
+    NSAssert([invalidSourceAttributes count] == 0, @"Cannot connect relationship: invalid attributes given for source entity '%@': %@", [[relationship entity] name], [[invalidSourceAttributes allObjects] componentsJoinedByString:@", "]);
+    NSSet *invalidDestinationAttributes = RKSetWithInvalidAttributesForEntity([attributes allValues], [relationship destinationEntity]);
+    NSAssert([invalidDestinationAttributes count] == 0, @"Cannot connect relationship: invalid attributes given for destination entity '%@': %@", [[relationship destinationEntity] name], [[invalidDestinationAttributes allObjects] componentsJoinedByString:@", "]);
+    
+    self = [[RKForeignKeyConnectionDescription alloc] init];
+    if (self) {
+        self.relationship = relationship;
+        self.attributes = attributes;
+    }
+    return self;
+}
+
+- (id)initWithRelationship:(NSRelationshipDescription *)relationship keyPath:(NSString *)keyPath
+{
+    NSParameterAssert(relationship);
+    NSParameterAssert(keyPath);
+    self = [[RKKeyPathConnectionDescription alloc] init];
+    if (self) {
+        self.relationship = relationship;
+        self.keyPath = keyPath;
+    }
+    return self;
+}
+
+- (id)init
+{
+    if ([self class] == [RKConnectionDescription class]) {
+        @throw [NSException exceptionWithName:NSInternalInconsistencyException
+                                       reason:[NSString stringWithFormat:@"%@ Failed to call designated initializer. "
+                                               "Invoke initWithRelationship:sourceKeyPath:destinationKeyPath:matcher: instead.",
+                                               NSStringFromClass([self class])]
+                                     userInfo:nil];
+    }
+    return [super init];
+}
+
+- (id)copyWithZone:(NSZone *)zone
+{
+    if ([self isForeignKeyConnection]) {
+        return [[[self class] allocWithZone:zone] initWithRelationship:self.relationship attributes:self.attributes];
+    } else if ([self isKeyPathConnection]) {
+        return [[[self class] allocWithZone:zone] initWithRelationship:self.relationship keyPath:self.keyPath];
+    }
+    
+    return nil;
+}
+
+- (BOOL)isForeignKeyConnection
+{
+    return NO;
+}
+
+- (BOOL)isKeyPathConnection
+{
+    return NO;
+}
+
+@end
+
+@implementation RKForeignKeyConnectionDescription
+
+- (BOOL)isForeignKeyConnection
+{
+    return YES;
+}
+
+- (NSString *)description
+{
+    return [NSString stringWithFormat:@"<%@:%p connecting Relationship '%@' from Entity '%@' to Destination Entity '%@' with attributes=%@>",
+            NSStringFromClass([self class]), self, [self.relationship name], [[self.relationship entity] name],
+            [[self.relationship destinationEntity] name], self.attributes];
+}
+
+@end
+
+@implementation RKKeyPathConnectionDescription
+
+- (BOOL)isKeyPathConnection
+{
+    return YES;
+}
+
+- (NSString *)description
+{
+    return [NSString stringWithFormat:@"<%@:%p connecting Relationship '%@' of Entity '%@' with keyPath=%@>",
+            NSStringFromClass([self class]), self, [self.relationship name], [[self.relationship entity] name], self.keyPath];
+}
+
+@end