Respond to CR.

// FREEBIE

Signal/src/ViewControllers/ExperienceUpgradesPageViewController.swift

@@ -526,7 +526,11 @@ class ExperienceUpgradesPageViewController: OWSViewController, UIPageViewControl
     }
 
     public func addViewController(experienceUpgrade: ExperienceUpgrade) {
-        guard let identifier = ExperienceUpgradeId(rawValue: experienceUpgrade.uniqueId) else {
+        guard let uniqueId = experienceUpgrade.uniqueId else {
+            Logger.error("\(self.TAG) experienceUpgrade is missing uniqueId.")
+            return
+        }
+        guard let identifier = ExperienceUpgradeId(rawValue: uniqueId) else {
             owsFail("\(TAG) unknown experience upgrade. skipping")
             return
         }

Signal/src/ViewControllers/MessageDetailViewController.swift

@@ -551,7 +551,11 @@ class MessageDetailViewController: OWSViewController, UIScrollViewDelegate {
         AssertIsOnMainThread()
 
         self.databaseConnection.read { transaction in
-            guard let newMessage = TSInteraction.fetch(uniqueId: self.message.uniqueId, transaction: transaction) as? TSMessage else {
+            guard let uniqueId = self.message.uniqueId else {
+                Logger.error("\(self.TAG) Message is missing uniqueId.")
+                return
+            }
+            guard let newMessage = TSInteraction.fetch(uniqueId: uniqueId, transaction: transaction) as? TSMessage else {
                 Logger.error("\(self.TAG) Couldn't reload message.")
                 return
             }
@@ -564,7 +568,11 @@ class MessageDetailViewController: OWSViewController, UIScrollViewDelegate {
 
         let notifications = self.databaseConnection.beginLongLivedReadTransaction()
 
-        guard self.databaseConnection.hasChange(forKey: message.uniqueId,
+        guard let uniqueId = self.message.uniqueId else {
+            Logger.error("\(self.TAG) Message is missing uniqueId.")
+            return
+        }
+        guard self.databaseConnection.hasChange(forKey: uniqueId,
                                                  inCollection: TSInteraction.collection(),
                                                  in: notifications) else {
                                                     Logger.debug("\(TAG) No relevant changes.")

Signal/src/environment/ExperienceUpgradeFinder.swift

@@ -59,7 +59,7 @@ class ExperienceUpgradeFinder: NSObject {
     // MARK: - Instance Methods
 
     public func allUnseen(transaction: YapDatabaseReadTransaction) -> [ExperienceUpgrade] {
-        return allExperienceUpgrades.filter { ExperienceUpgrade.fetch(uniqueId: $0.uniqueId, transaction: transaction) == nil }
+        return allExperienceUpgrades.filter { ExperienceUpgrade.fetch(uniqueId: $0.uniqueId!, transaction: transaction) == nil }
     }
 
     public func markAllAsSeen(transaction: YapDatabaseReadWriteTransaction) {

Signal/src/environment/ExperienceUpgrades/ExperienceUpgrade.swift

@@ -16,7 +16,7 @@ class ExperienceUpgrade: TSYapDatabaseObject {
         super.init(uniqueId: uniqueId)
     }
 
-    override required init(uniqueId: String) {
+    override required init(uniqueId: String?) {
         // This is the unfortunate seam between strict swift and fast-and-loose objc
         // we can't leave these properties nil, since we really "don't know" that the superclass
         // will assign them.

SignalServiceKit/src/Contacts/OWSDisappearingMessagesConfiguration.m

@@ -27,7 +27,7 @@ const uint32_t OWSDisappearingMessagesConfigurationDefaultExpirationDuration = k
                   durationSeconds:OWSDisappearingMessagesConfigurationDefaultExpirationDuration];
 }
 
-- (instancetype)initWithCoder:(NSCoder *)coder
+- (nullable instancetype)initWithCoder:(NSCoder *)coder
 {
     self = [super initWithCoder:coder];
 

SignalServiceKit/src/Contacts/TSThread.h

@@ -156,28 +156,8 @@ NS_ASSUME_NONNULL_BEGIN
 @property (atomic, readonly) BOOL isMuted;
 @property (atomic, readonly, nullable) NSDate *mutedUntilDate;
 
-// This model may be updated from many threads. We don't want to save
-// our local copy (this instance) since it may be out of date.  We also
-// want to avoid re-saving a model that has been deleted.  Therefore, we
-// use these "updateWith..." methods to:
-//
-// a) Update a property of this instance.
-// b) If a copy of this model exists in the database, load an up-to-date copy,
-//    and update and save that copy.
-// b) If a copy of this model _DOES NOT_ exist in the database, do _NOT_ save
-//    this local instance.
-//
-// After "updateWith...":
-//
-// a) An copy of this model in the database will have been updated.
-// b) The local property on this instance will always have been updated.
-// c) Other properties on this instance may be out of date.
-//
-// All mutable properties of this class have been made read-only to
-// prevent accidentally modifying them directly.
-//
-// This isn't a perfect arrangement, but in practice this will prevent
-// data loss and will resolve all known issues.
+#pragma mark - Update With... Methods
+
 - (void)updateWithMutedUntilDate:(NSDate *)mutedUntilDate;
 
 @end

SignalServiceKit/src/Contacts/TSThread.m

@@ -34,7 +34,8 @@ NS_ASSUME_NONNULL_BEGIN
     return @"TSThread";
 }
 
-- (instancetype)initWithUniqueId:(NSString *)uniqueId {
+- (instancetype)initWithUniqueId:(NSString *_Nullable)uniqueId
+{
     self = [super initWithUniqueId:uniqueId];
 
     if (self) {
@@ -382,30 +383,15 @@ NS_ASSUME_NONNULL_BEGIN
             [mutedUntilDate timeIntervalSinceDate:now] > 0);
 }
 
-// This method does the work for the "updateWith..." methods.  Please see
-// the header for a discussion of those methods.
-- (void)applyChangeToSelfAndLatestThread:(YapDatabaseReadWriteTransaction *)transaction
-                             changeBlock:(void (^)(TSThread *))changeBlock
-{
-    OWSAssert(transaction);
-    
-    changeBlock(self);
-    
-    NSString *collection = [[self class] collection];
-    TSThread *latestInstance = [transaction objectForKey:self.uniqueId inCollection:collection];
-    if (latestInstance) {
-        changeBlock(latestInstance);
-        [latestInstance saveWithTransaction:transaction];
-    }
-}
+#pragma mark - Update With... Methods
 
 - (void)updateWithMutedUntilDate:(NSDate *)mutedUntilDate
 {
     [self.dbReadWriteConnection readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
-        [self applyChangeToSelfAndLatestThread:transaction
-                                   changeBlock:^(TSThread *thread) {
-                                       [thread setMutedUntilDate:mutedUntilDate];
-                                   }];
+        [self applyChangeToSelfAndLatestCopy:transaction
+                                 changeBlock:^(TSThread *thread) {
+                                     [thread setMutedUntilDate:mutedUntilDate];
+                                 }];
     }];
 }
 

SignalServiceKit/src/Messages/Interactions/TSMessage.h

@@ -56,30 +56,8 @@ NS_ASSUME_NONNULL_BEGIN
 - (BOOL)shouldStartExpireTimer;
 - (BOOL)shouldStartExpireTimer:(YapDatabaseReadTransaction *)transaction;
 
-#pragma mark - Update Methods
+#pragma mark - Update With... Methods
 
-// This model may be updated from many threads. We don't want to save
-// our local copy (this instance) since it may be out of date.  We also
-// want to avoid re-saving a model that has been deleted.  Therefore, we
-// use these "updateWith..." methods to:
-//
-// a) Update a property of this instance.
-// b) If a copy of this model exists in the database, load an up-to-date copy,
-//    and update and save that copy.
-// b) If a copy of this model _DOES NOT_ exist in the database, do _NOT_ save
-//    this local instance.
-//
-// After "updateWith...":
-//
-// a) An copy of this model in the database will have been updated.
-// b) The local property on this instance will always have been updated.
-// c) Other properties on this instance may be out of date.
-//
-// All mutable properties of this class have been made read-only to
-// prevent accidentally modifying them directly.
-//
-// This isn't a perfect arrangement, but in practice this will prevent
-// data loss and will resolve all known issues.
 - (void)updateWithExpireStartedAt:(uint64_t)expireStartedAt transaction:(YapDatabaseReadWriteTransaction *)transaction;
 
 @end

SignalServiceKit/src/Messages/Interactions/TSMessage.m

@@ -281,33 +281,16 @@ static const NSUInteger OWSMessageSchemaVersion = 3;
     return YES;
 }
 
-#pragma mark - Update Methods
-
-// This method does the work for the "updateWith..." methods.  Please see
-// the header for a discussion of those methods.
-- (void)applyChangeToSelfAndLatestMessage:(YapDatabaseReadWriteTransaction *)transaction
-                              changeBlock:(void (^)(TSMessage *))changeBlock
-{
-    OWSAssert(transaction);
-
-    changeBlock(self);
-
-    NSString *collection = [[self class] collection];
-    TSMessage *latestMessage = [transaction objectForKey:self.uniqueId inCollection:collection];
-    if (latestMessage) {
-        changeBlock(latestMessage);
-        [latestMessage saveWithTransaction:transaction];
-    }
-}
+#pragma mark - Update With... Methods
 
 - (void)updateWithExpireStartedAt:(uint64_t)expireStartedAt transaction:(YapDatabaseReadWriteTransaction *)transaction
 {
     OWSAssert(expireStartedAt > 0);
 
-    [self applyChangeToSelfAndLatestMessage:transaction
-                                changeBlock:^(TSMessage *message) {
-                                    [message setExpireStartedAt:expireStartedAt];
-                                }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSMessage *message) {
+                                 [message setExpireStartedAt:expireStartedAt];
+                             }];
 }
 
 @end

SignalServiceKit/src/Messages/Interactions/TSOutgoingMessage.h

@@ -148,28 +148,8 @@ typedef NS_ENUM(NSInteger, TSGroupMetaMessage) {
 - (OWSSignalServiceProtosAttachmentPointer *)buildAttachmentProtoForAttachmentId:(NSString *)attachmentId
                                                                         filename:(nullable NSString *)filename;
 
-// This model may be updated from many threads. We don't want to save
-// our local copy (this instance) since it may be out of date.  We also
-// want to avoid re-saving a model that has been deleted.  Therefore, we
-// use these "updateWith..." methods to:
-//
-// a) Update a property of this instance.
-// b) If a copy of this model exists in the database, load an up-to-date copy,
-//    and update and save that copy.
-// b) If a copy of this model _DOES NOT_ exist in the database, do _NOT_ save
-//    this local instance.
-//
-// After "updateWith...":
-//
-// a) An copy of this model in the database will have been updated.
-// b) The local property on this instance will always have been updated.
-// c) Other properties on this instance may be out of date.
-//
-// All mutable properties of this class have been made read-only to
-// prevent accidentally modifying them directly.
-//
-// This isn't a perfect arrangement, but in practice this will prevent
-// data loss and will resolve all known issues.
+#pragma mark - Update With... Methods
+
 - (void)updateWithMessageState:(TSOutgoingMessageState)messageState;
 - (void)updateWithMessageState:(TSOutgoingMessageState)messageState
                    transaction:(YapDatabaseReadWriteTransaction *)transaction;

SignalServiceKit/src/Messages/Interactions/TSOutgoingMessage.m

@@ -238,35 +238,18 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
     return OWSInteractionType_OutgoingMessage;
 }
 
-#pragma mark - Update Methods
-
-// This method does the work for the "updateWith..." methods.  Please see
-// the header for a discussion of those methods.
-- (void)applyChangeToSelfAndLatestOutgoingMessage:(YapDatabaseReadWriteTransaction *)transaction
-                                      changeBlock:(void (^)(TSOutgoingMessage *))changeBlock
-{
-    OWSAssert(transaction);
-
-    changeBlock(self);
-
-    NSString *collection = [[self class] collection];
-    TSOutgoingMessage *latestMessage = [transaction objectForKey:self.uniqueId inCollection:collection];
-    if (latestMessage) {
-        changeBlock(latestMessage);
-        [latestMessage saveWithTransaction:transaction];
-    }
-}
+#pragma mark - Update With... Methods
 
 - (void)updateWithSendingError:(NSError *)error
 {
     OWSAssert(error);
 
     [self.dbReadWriteConnection readWriteWithBlock:^(YapDatabaseReadWriteTransaction *transaction) {
-        [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                            changeBlock:^(TSOutgoingMessage *message) {
-                                                [message setMessageState:TSOutgoingMessageStateUnsent];
-                                                [message setMostRecentFailureText:error.localizedDescription];
-                                            }];
+        [self applyChangeToSelfAndLatestCopy:transaction
+                                 changeBlock:^(TSOutgoingMessage *message) {
+                                     [message setMessageState:TSOutgoingMessageStateUnsent];
+                                     [message setMostRecentFailureText:error.localizedDescription];
+                                 }];
     }];
 }
 
@@ -282,19 +265,19 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
 {
     OWSAssert(transaction);
 
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            [message setMessageState:messageState];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 [message setMessageState:messageState];
+                             }];
 }
 
 - (void)updateWithHasSyncedTranscript:(BOOL)hasSyncedTranscript
                           transaction:(YapDatabaseReadWriteTransaction *)transaction
 {
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            [message setHasSyncedTranscript:hasSyncedTranscript];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 [message setHasSyncedTranscript:hasSyncedTranscript];
+                             }];
 }
 
 - (void)updateWithCustomMessage:(NSString *)customMessage transaction:(YapDatabaseReadWriteTransaction *)transaction
@@ -302,10 +285,10 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
     OWSAssert(customMessage);
     OWSAssert(transaction);
 
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            [message setCustomMessage:customMessage];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 [message setCustomMessage:customMessage];
+                             }];
 }
 
 - (void)updateWithCustomMessage:(NSString *)customMessage
@@ -322,32 +305,31 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
     OWSAssert(recipientId.length > 0);
     OWSAssert(transaction);
 
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
 
-                                            if (deliveryTimestamp) {
-                                                NSMutableDictionary<NSString *, NSNumber *> *recipientDeliveryMap
-                                                    = (message.recipientDeliveryMap
-                                                            ? [message.recipientDeliveryMap mutableCopy]
-                                                            : [NSMutableDictionary new]);
-                                                recipientDeliveryMap[recipientId] = deliveryTimestamp;
-                                                message.recipientDeliveryMap = [recipientDeliveryMap copy];
-                                            }
+                                 if (deliveryTimestamp) {
+                                     NSMutableDictionary<NSString *, NSNumber *> *recipientDeliveryMap
+                                         = (message.recipientDeliveryMap ? [message.recipientDeliveryMap mutableCopy]
+                                                                         : [NSMutableDictionary new]);
+                                     recipientDeliveryMap[recipientId] = deliveryTimestamp;
+                                     message.recipientDeliveryMap = [recipientDeliveryMap copy];
+                                 }
 
-                                            [message setWasDelivered:YES];
-                                        }];
+                                 [message setWasDelivered:YES];
+                             }];
 }
 
 - (void)updateWithWasSentFromLinkedDeviceWithTransaction:(YapDatabaseReadWriteTransaction *)transaction
 {
     OWSAssert(transaction);
 
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            [message setMessageState:TSOutgoingMessageStateSentToService];
-                                            [message setWasDelivered:YES];
-                                            [message setIsFromLinkedDevice:YES];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 [message setMessageState:TSOutgoingMessageStateSentToService];
+                                 [message setWasDelivered:YES];
+                                 [message setIsFromLinkedDevice:YES];
+                             }];
 }
 
 - (void)updateWithSingleGroupRecipient:(NSString *)singleGroupRecipient
@@ -356,10 +338,10 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
     OWSAssert(transaction);
     OWSAssert(singleGroupRecipient.length > 0);
 
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            [message setSingleGroupRecipient:singleGroupRecipient];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 [message setSingleGroupRecipient:singleGroupRecipient];
+                             }];
 }
 
 #pragma mark - Sent Recipients
@@ -411,10 +393,10 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
 - (void)updateWithSentRecipient:(NSString *)contactId transaction:(YapDatabaseReadWriteTransaction *)transaction
 {
     OWSAssert(transaction);
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            [message addSentRecipient:contactId];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 [message addSentRecipient:contactId];
+                             }];
 }
 
 - (void)updateWithReadRecipientId:(NSString *)recipientId
@@ -424,14 +406,14 @@ NSString *const kTSOutgoingMessageSentRecipientAll = @"kTSOutgoingMessageSentRec
     OWSAssert(recipientId.length > 0);
     OWSAssert(transaction);
 
-    [self applyChangeToSelfAndLatestOutgoingMessage:transaction
-                                        changeBlock:^(TSOutgoingMessage *message) {
-                                            NSMutableDictionary<NSString *, NSNumber *> *recipientReadMap
-                                                = (message.recipientReadMap ? [message.recipientReadMap mutableCopy]
-                                                                            : [NSMutableDictionary new]);
-                                            recipientReadMap[recipientId] = @(readTimestamp);
-                                            message.recipientReadMap = [recipientReadMap copy];
-                                        }];
+    [self applyChangeToSelfAndLatestCopy:transaction
+                             changeBlock:^(TSOutgoingMessage *message) {
+                                 NSMutableDictionary<NSString *, NSNumber *> *recipientReadMap
+                                     = (message.recipientReadMap ? [message.recipientReadMap mutableCopy]
+                                                                 : [NSMutableDictionary new]);
+                                 recipientReadMap[recipientId] = @(readTimestamp);
+                                 message.recipientReadMap = [recipientReadMap copy];
+                             }];
 }
 
 - (nullable NSNumber *)firstRecipientReadTimestamp

SignalServiceKit/src/Messages/OWSBatchMessageProcessor.m

@@ -30,7 +30,7 @@ NS_ASSUME_NONNULL_BEGIN
 - (instancetype)initWithEnvelopeData:(NSData *)envelopeData
                        plaintextData:(NSData *_Nullable)plaintextData NS_DESIGNATED_INITIALIZER;
 - (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
-- (instancetype)initWithUniqueId:(NSString *)uniqueId NS_UNAVAILABLE;
+- (instancetype)initWithUniqueId:(NSString *_Nullable)uniqueId NS_UNAVAILABLE;
 - (OWSSignalServiceProtosEnvelope *)envelopeProto;
 
 @end

SignalServiceKit/src/Messages/OWSMessageReceiver.m

@@ -25,7 +25,7 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)initWithEnvelope:(OWSSignalServiceProtosEnvelope *)envelope NS_DESIGNATED_INITIALIZER;
 - (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
-- (instancetype)initWithUniqueId:(NSString *)uniqueId NS_UNAVAILABLE;
+- (instancetype)initWithUniqueId:(NSString *_Nullable)uniqueId NS_UNAVAILABLE;
 - (OWSSignalServiceProtosEnvelope *)envelopeProto;
 
 @end

SignalServiceKit/src/Security/OWSRecipientIdentity.h

@@ -31,7 +31,7 @@ OWSSignalServiceProtosVerifiedState OWSVerificationStateToProtoState(OWSVerifica
 
 #pragma mark - Initializers
 
-- (instancetype)initWithUniqueId:(NSString *)uniqueId NS_UNAVAILABLE;
+- (instancetype)initWithUniqueId:(NSString *_Nullable)uniqueId NS_UNAVAILABLE;
 
 - (instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
 

SignalServiceKit/src/Storage/TSYapDatabaseObject.h

@@ -4,6 +4,8 @@
 
 #import <Mantle/MTLModel+NSCoding.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class TSStorageManager;
 @class YapDatabaseConnection;
 @class YapDatabaseReadTransaction;
@@ -18,8 +20,8 @@
  *
  *  @return Initialized object
  */
-- (instancetype)initWithUniqueId:(NSString *)uniqueId NS_DESIGNATED_INITIALIZER;
-- (instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
+- (instancetype)initWithUniqueId:(NSString *_Nullable)uniqueId NS_DESIGNATED_INITIALIZER;
+- (nullable instancetype)initWithCoder:(NSCoder *)coder NS_DESIGNATED_INITIALIZER;
 
 /**
  *  Returns the collection to which the object belongs.
@@ -77,8 +79,11 @@
  *
  *  @return Instance of the object or nil if non-existent
  */
-+ (instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID transaction:(YapDatabaseReadTransaction *)transaction NS_SWIFT_NAME(fetch(uniqueId:transaction:));
-+ (instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID NS_SWIFT_NAME(fetch(uniqueId:));
++ (nullable instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID
+                                     transaction:(YapDatabaseReadTransaction *)transaction
+    NS_SWIFT_NAME(fetch(uniqueId:transaction
+:));
++ (nullable instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID NS_SWIFT_NAME(fetch(uniqueId:));
 
 /**
  * Saves the object with the shared readWrite connection.
@@ -113,9 +118,40 @@
 /**
  *  The unique identifier of the stored object
  */
-@property (nonatomic) NSString *uniqueId;
+@property (nonatomic, nullable) NSString *uniqueId;
 
 - (void)removeWithTransaction:(YapDatabaseReadWriteTransaction *)transaction;
 - (void)remove;
 
+#pragma mark Update With...
+
+// This method is used by "updateWith..." methods.
+//
+// This model may be updated from many threads. We don't want to save
+// our local copy (this instance) since it may be out of date.  We also
+// want to avoid re-saving a model that has been deleted.  Therefore, we
+// use "updateWith..." methods to:
+//
+// a) Update a property of this instance.
+// b) If a copy of this model exists in the database, load an up-to-date copy,
+//    and update and save that copy.
+// b) If a copy of this model _DOES NOT_ exist in the database, do _NOT_ save
+//    this local instance.
+//
+// After "updateWith...":
+//
+// a) Any copy of this model in the database will have been updated.
+// b) The local property on this instance will always have been updated.
+// c) Other properties on this instance may be out of date.
+//
+// All mutable properties of this class have been made read-only to
+// prevent accidentally modifying them directly.
+//
+// This isn't a perfect arrangement, but in practice this will prevent
+// data loss and will resolve all known issues.
+- (void)applyChangeToSelfAndLatestCopy:(YapDatabaseReadWriteTransaction *)transaction
+                           changeBlock:(void (^)(id))changeBlock;
+
 @end
+
+NS_ASSUME_NONNULL_END

SignalServiceKit/src/Storage/TSYapDatabaseObject.m

@@ -6,6 +6,8 @@
 #import "TSStorageManager.h"
 #import <YapDatabase/YapDatabaseTransaction.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation TSYapDatabaseObject
 
 - (instancetype)init
@@ -13,7 +15,7 @@
     return [self initWithUniqueId:[[NSUUID UUID] UUIDString]];
 }
 
-- (instancetype)initWithUniqueId:(NSString *)aUniqueId
+- (instancetype)initWithUniqueId:(NSString *_Nullable)aUniqueId
 {
     self = [super init];
     if (!self) {
@@ -25,6 +27,11 @@
     return self;
 }
 
+- (nullable instancetype)initWithCoder:(NSCoder *)coder
+{
+    return [super initWithCoder:coder];
+}
+
 - (void)saveWithTransaction:(YapDatabaseReadWriteTransaction *)transaction
 {
     [transaction setObject:self forKey:self.uniqueId inCollection:[[self class] collection]];
@@ -176,18 +183,40 @@
     }];
 }
 
-+ (instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID transaction:(YapDatabaseReadTransaction *)transaction
++ (nullable instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID
+                                     transaction:(YapDatabaseReadTransaction *)transaction
 {
     return [transaction objectForKey:uniqueID inCollection:[self collection]];
 }
 
-+ (instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID
++ (nullable instancetype)fetchObjectWithUniqueID:(NSString *)uniqueID
 {
-    __block id object;
+    __block id _Nullable object = nil;
     [[self dbReadConnection] readWithBlock:^(YapDatabaseReadTransaction *transaction) {
         object = [transaction objectForKey:uniqueID inCollection:[self collection]];
     }];
     return object;
 }
 
+#pragma mark Update With...
+
+// This method does the work for the "updateWith..." methods.  Please see
+// the header for a discussion of those methods.
+- (void)applyChangeToSelfAndLatestCopy:(YapDatabaseReadWriteTransaction *)transaction
+                           changeBlock:(void (^)(id))changeBlock
+{
+    OWSAssert(transaction);
+
+    changeBlock(self);
+
+    NSString *collection = [[self class] collection];
+    id latestInstance = [transaction objectForKey:self.uniqueId inCollection:collection];
+    if (latestInstance) {
+        changeBlock(latestInstance);
+        [latestInstance saveWithTransaction:transaction];
+    }
+}
+
 @end
+
+NS_ASSUME_NONNULL_END