diff --git a/RealmCrust.xcodeproj/project.pbxproj b/RealmCrust.xcodeproj/project.pbxproj
index 0880b29..9ddd98e 100644
--- a/RealmCrust.xcodeproj/project.pbxproj
+++ b/RealmCrust.xcodeproj/project.pbxproj
@@ -7,6 +7,7 @@
 	objects = {
 
 /* Begin PBXBuildFile section */
+		173E0D821C6C27CB00A9E9B3 /* PrimaryKeyTests.swift in Sources */ = {isa = PBXBuildFile; fileRef = 173E0D811C6C27CB00A9E9B3 /* PrimaryKeyTests.swift */; };
 		175C9A611C36201F00B0D6E7 /* RealmCrust.h in Headers */ = {isa = PBXBuildFile; fileRef = 175C9A601C36201F00B0D6E7 /* RealmCrust.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		175C9A681C36201F00B0D6E7 /* RealmCrust.framework in Frameworks */ = {isa = PBXBuildFile; fileRef = 175C9A5D1C36201F00B0D6E7 /* RealmCrust.framework */; };
 		175C9A781C36247700B0D6E7 /* RealmMappings.swift in Sources */ = {isa = PBXBuildFile; fileRef = 175C9A771C36247700B0D6E7 /* RealmMappings.swift */; };
@@ -34,6 +35,7 @@
 
 /* Begin PBXFileReference section */
 		0E234D4DFBBC77280B5A7F0C /* Pods-RealmCrustTests.debug.xcconfig */ = {isa = PBXFileReference; includeInIndex = 1; lastKnownFileType = text.xcconfig; name = "Pods-RealmCrustTests.debug.xcconfig"; path = "Pods/Target Support Files/Pods-RealmCrustTests/Pods-RealmCrustTests.debug.xcconfig"; sourceTree = "<group>"; };
+		173E0D811C6C27CB00A9E9B3 /* PrimaryKeyTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = PrimaryKeyTests.swift; sourceTree = "<group>"; };
 		175C9A5D1C36201F00B0D6E7 /* RealmCrust.framework */ = {isa = PBXFileReference; explicitFileType = wrapper.framework; includeInIndex = 0; path = RealmCrust.framework; sourceTree = BUILT_PRODUCTS_DIR; };
 		175C9A601C36201F00B0D6E7 /* RealmCrust.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = RealmCrust.h; sourceTree = "<group>"; };
 		175C9A621C36201F00B0D6E7 /* Info.plist */ = {isa = PBXFileReference; lastKnownFileType = text.plist.xml; path = Info.plist; sourceTree = "<group>"; };
@@ -117,6 +119,7 @@
 				175C9A7E1C38547700B0D6E7 /* EmployeeMappingTests.swift */,
 				175C9A7F1C38547700B0D6E7 /* EmployeeStub.swift */,
 				175C9A871C38548000B0D6E7 /* Operators.swift */,
+				173E0D811C6C27CB00A9E9B3 /* PrimaryKeyTests.swift */,
 				175C9A891C38548000B0D6E7 /* RealmMappingTest.swift */,
 				175C9A6E1C36201F00B0D6E7 /* Info.plist */,
 			);
@@ -346,6 +349,7 @@
 				175C9A8E1C38548000B0D6E7 /* RealmMappingTest.swift in Sources */,
 				175C9A841C38547700B0D6E7 /* Employee.swift in Sources */,
 				175C9A821C38547700B0D6E7 /* CompanyStub.swift in Sources */,
+				173E0D821C6C27CB00A9E9B3 /* PrimaryKeyTests.swift in Sources */,
 				175C9A861C38547700B0D6E7 /* EmployeeStub.swift in Sources */,
 				175C9A811C38547700B0D6E7 /* CompanyMappingTests.swift in Sources */,
 				175C9A851C38547700B0D6E7 /* EmployeeMappingTests.swift in Sources */,
diff --git a/RealmCrust/RealmMappings.swift b/RealmCrust/RealmMappings.swift
index 1428a5c..598ef46 100644
--- a/RealmCrust/RealmMappings.swift
+++ b/RealmCrust/RealmMappings.swift
@@ -4,12 +4,14 @@ import RealmSwift
 public class RealmAdaptor {
     
     public typealias BaseType = Object
-    public typealias ResultsType = Results<Object>
+    public typealias ResultsType = Set<BaseType>
     
     var realm: Realm
+    var cache: NSMutableSet
     
     public init(realm: Realm) {
         self.realm = realm
+        self.cache = []
     }
     
     public convenience init() throws {
@@ -22,22 +24,26 @@ public class RealmAdaptor {
     
     public func mappingEnded() throws {
         try self.realm.commitWrite()
+        self.cache.removeAllObjects()
     }
     
     public func mappingErrored(error: ErrorType) {
         if self.realm.inWriteTransaction {
             self.realm.cancelWrite()
         }
+        self.cache.removeAllObjects()
     }
     
     public func createObject(objType: BaseType.Type) throws -> BaseType {
         let obj = objType.init()
+        self.cache.addObject(obj)
         return obj
     }
     
     public func saveObjects(objects: [BaseType]) throws {
         let saveBlock = {
             for obj in objects {
+                self.cache.removeObject(obj)
                 self.realm.add(objects, update: obj.dynamicType.primaryKey() != nil)
             }
         }
@@ -50,6 +56,7 @@ public class RealmAdaptor {
     
     public func deleteObject(obj: BaseType) throws {
         let deleteBlock = {
+            self.cache.removeObject(obj)
             self.realm.delete(obj)
         }
         if self.realm.inWriteTransaction {
@@ -74,12 +81,17 @@ public class RealmAdaptor {
     
     public func fetchObjectsWithType(type: BaseType.Type, predicate: NSPredicate) -> ResultsType? {
         
+        let objects = self.cache.filteredSetUsingPredicate(predicate)
+        if objects.count > 0 {
+            return objects as? ResultsType
+        }
+        
         if type.primaryKey() != nil {
             // We're going to build an unstored object and update when saving based on the primary key.
             return nil
         }
         
-        return realm.objects(type).filter(predicate)
+        return Set(realm.objects(type).filter(predicate))
     }
 }
 
diff --git a/RealmCrustTests/PrimaryKeyTests.swift b/RealmCrustTests/PrimaryKeyTests.swift
new file mode 100644
index 0000000..a4dc01b
--- /dev/null
+++ b/RealmCrustTests/PrimaryKeyTests.swift
@@ -0,0 +1,112 @@
+import XCTest
+import Crust
+import JSONValueRX
+import RealmCrust
+import RealmSwift
+
+class PrimaryObj1: Object {
+    let class2s = List<PrimaryObj2>()
+    dynamic var uuid: String = ""
+    
+    override class func primaryKey() -> String? {
+        return "uuid"
+    }
+}
+
+class PrimaryObj2: Object {
+    dynamic var uuid: String = ""
+    dynamic var class1: PrimaryObj1?
+    
+    override class func primaryKey() -> String? {
+        return "uuid"
+    }
+}
+
+class PrimaryObj1Mapping : RealmMapping {
+    
+    var adaptor: RealmAdaptor
+    var primaryKeys: Dictionary<String, CRMappingKey>? {
+        return [ "uuid" : "data.uuid" ]
+    }
+    
+    required init(adaptor: RealmAdaptor) {
+        self.adaptor = adaptor
+    }
+    
+    func mapping(inout tomap: PrimaryObj1, context: MappingContext) {
+        let obj2Mapping = PrimaryObj2Mapping(adaptor: self.adaptor)
+        
+        tomap.class2s       <- KeyExtensions.Mapping("class2s", obj2Mapping) >*<
+        tomap.uuid          <- "data.uuid" >*<
+        context
+    }
+}
+
+// Until we support optional mappings, have to make a nested version.
+class NestedPrimaryObj1Mapping : RealmMapping {
+    
+    var adaptor: RealmAdaptor
+    var primaryKeys: Dictionary<String, CRMappingKey>? {
+        return [ "uuid" : "data.uuid" ]
+    }
+    
+    required init(adaptor: RealmAdaptor) {
+        self.adaptor = adaptor
+    }
+    
+    func mapping(inout tomap: PrimaryObj1, context: MappingContext) {
+        tomap.uuid          <- "data.uuid" >*<
+        context
+    }
+}
+
+class PrimaryObj2Mapping : RealmMapping {
+    
+    var adaptor: RealmAdaptor
+    var primaryKeys: Dictionary<String, CRMappingKey>? {
+        return [ "uuid" : "data.more_data.uuid" ]
+    }
+    
+    required init(adaptor: RealmAdaptor) {
+        self.adaptor = adaptor
+    }
+    
+    func mapping(inout tomap: PrimaryObj2, context: MappingContext) {
+        // TODO: Including this mapping fails. Need to support making some mappings as optional
+        // so when the recursive cycle of json between these two relationships runs out it doesn't error
+        // from expecting json.
+        //
+        // In the meantime, user can write separate Nested Mappings for the top level object and nested objects.
+//        let obj1Mapping = PrimaryObj1Mapping(adaptor: self.adaptor)
+        
+        let obj1Mapping = NestedPrimaryObj1Mapping(adaptor: self.adaptor)
+        
+        tomap.class1        <- KeyExtensions.Mapping("class1", obj1Mapping) >*<
+        tomap.uuid          <- "data.more_data.uuid" >*<
+        context
+    }
+}
+
+class PrimaryKeyTests: RealmMappingTest {
+
+    func testMappingsWithPrimaryKeys() {
+        
+        var json1Dict = [ "data" : [ "uuid" : "primary1" ] ] as [ String : AnyObject ]
+        let json2Dict1 = [ "data.more_data.uuid" : "primary2.1", "class1" : json1Dict ]
+        let json2Dict2 = [ "data.more_data.uuid" : "primary2.2", "class1" : json1Dict ]
+        
+        json1Dict["class2s"] = [ json2Dict1, json2Dict2 ]
+        
+        XCTAssertEqual(realm!.objects(PrimaryObj1).count, 0)
+        XCTAssertEqual(realm!.objects(PrimaryObj2).count, 0)
+        
+        let json = try! JSONValue(object: json1Dict)
+        let mapper = CRMapper<PrimaryObj1, PrimaryObj1Mapping>()
+        let object = try! mapper.mapFromJSONToExistingObject(json, mapping: PrimaryObj1Mapping(adaptor: adaptor!))
+        
+        XCTAssertEqual(realm!.objects(PrimaryObj1).count, 1)
+        XCTAssertEqual(realm!.objects(PrimaryObj2).count, 2)
+        XCTAssertEqual(object.uuid, "primary1")
+        XCTAssertEqual(object.class2s.count, 2)
+    }
+}