optimizations

Sources/DataStack+DataSources.swift

@@ -52,7 +52,8 @@ extension DataStack {
      */
     public func publishObject<O: DynamicObject>(_ objectID: O.ObjectID) -> ObjectPublisher<O> {
 
-        return ObjectPublisher<O>(objectID: objectID, context: self.unsafeContext())
+        let context = self.unsafeContext()
+        return context.objectPublisher(objectID: objectID)
     }
     
     /**

Sources/Internals.DiffableDataSourceSnapshot.swift

@@ -121,6 +121,16 @@ extension Internals {
             return self.structure.allSectionIDs.firstIndex(of: identifier)
         }
 
+        func isReloaded(sectionID: String) -> Bool? {
+
+            return self.structure.isReloaded(sectionID: sectionID)
+        }
+
+        func isReloaded(itemID: NSManagedObjectID) -> Bool? {
+
+            return self.structure.isReloaded(itemID: itemID)
+        }
+
         mutating func appendItems(_ identifiers: [NSManagedObjectID], toSection sectionIdentifier: String?) {
 
             self.structure.append(itemIDs: identifiers, to: sectionIdentifier)
@@ -329,6 +339,24 @@ extension Internals {
                 return self.sections.lazy.flatMap({ $0.elements }).map({ $0.differenceIdentifier })
             }
 
+            func isReloaded(sectionID: String) -> Bool? {
+
+                return self.sections.first(where: { $0.differenceIdentifier == sectionID })?.isReloaded
+            }
+
+            func isReloaded(itemID: NSManagedObjectID) -> Bool? {
+
+                for section in self.sections {
+
+                    guard let item = section.elements.first(where: { $0.differenceIdentifier == itemID }) else {
+
+                        return nil
+                    }
+                    return item.isReloaded
+                }
+                return nil
+            }
+
             func items(in sectionID: String) -> [NSManagedObjectID] {
 
                 guard let sectionIndex = self.sectionIndex(of: sectionID) else {
@@ -340,7 +368,7 @@ extension Internals {
 
             func section(containing itemID: NSManagedObjectID) -> String? {
 
-                return self.itemPositionMap()[itemID]?.section.differenceIdentifier
+                return self.itemPositionMap(itemID)?.section.differenceIdentifier
             }
 
             mutating func append(itemIDs: [NSManagedObjectID], to sectionID: String?) {
@@ -369,7 +397,7 @@ extension Internals {
 
             mutating func insert(itemIDs: [NSManagedObjectID], before beforeItemID: NSManagedObjectID) {
 
-                guard let itemPosition = self.itemPositionMap()[beforeItemID] else {
+                guard let itemPosition = self.itemPositionMap(beforeItemID) else {
 
                     Internals.abort("Item \(beforeItemID) does not exist")
                 }
@@ -380,7 +408,7 @@ extension Internals {
 
             mutating func insert(itemIDs: [NSManagedObjectID], after afterItemID: NSManagedObjectID) {
 
-                guard let itemPosition = self.itemPositionMap()[afterItemID] else {
+                guard let itemPosition = self.itemPositionMap(afterItemID) else {
 
                     Internals.abort("Item \(afterItemID) does not exist")
                 }
@@ -433,7 +461,7 @@ extension Internals {
 
                     Internals.abort("Item \(itemID) does not exist")
                 }
-                guard let itemPosition = self.itemPositionMap()[beforeItemID] else {
+                guard let itemPosition = self.itemPositionMap(beforeItemID) else {
 
                     Internals.abort("Item \(beforeItemID) does not exist")
                 }
@@ -447,7 +475,7 @@ extension Internals {
 
                     Internals.abort("Item \(itemID) does not exist")
                 }
-                guard let itemPosition = self.itemPositionMap()[afterItemID] else {
+                guard let itemPosition = self.itemPositionMap(afterItemID) else {
 
                     Internals.abort("Item \(afterItemID) does not exist")
                 }
@@ -556,7 +584,7 @@ extension Internals {
             @discardableResult
             private mutating func remove(itemID: NSManagedObjectID) -> Item? {
 
-                guard let itemPosition = self.itemPositionMap()[itemID] else {
+                guard let itemPosition = self.itemPositionMap(itemID) else {
 
                     return nil
                 }
@@ -574,6 +602,28 @@ extension Internals {
                 return self.sections.remove(at: sectionIndex)
             }
 
+            private func itemPositionMap(_ itemID: NSManagedObjectID) -> ItemPosition? {
+
+                let sections = self.sections
+                for (sectionIndex, section) in sections.enumerated() {
+
+                    for (itemRelativeIndex, item) in section.elements.enumerated() {
+
+                        guard item.differenceIdentifier == itemID else {
+
+                            continue
+                        }
+                        return ItemPosition(
+                            item: item,
+                            itemRelativeIndex: itemRelativeIndex,
+                            section: section,
+                            sectionIndex: sectionIndex
+                        )
+                    }
+                }
+                return nil
+            }
+
             private func itemPositionMap() -> [NSManagedObjectID: ItemPosition] {
 
                 return self.sections.enumerated().reduce(into: [:]) { result, section in

Sources/ListSnapshot.swift

@@ -214,6 +214,28 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
         return snapshot.numberOfItems(inSection: sectionID) > 0
     }
 
+    /**
+     Checks if the `ListSnapshot` has changes in the specified section.
+
+     - parameter sectionID: the section identifier. Using an index outside the valid range will return `nil`.
+     - returns: `true` if the specified section has changes, `false` if no changes, or `nil` if the `sectionID` does not exist
+     */
+    public func hasChanges(sectionID: String) -> Bool? {
+
+        return self.diffableSnapshot.isReloaded(sectionID: sectionID)
+    }
+
+    /**
+     Checks if the `ListSnapshot` has changes for the specified item.
+
+     - parameter itemID: the item identifier. Using an index outside the valid range will return `nil`.
+     - returns: `true` if the specified item has changes, `false` if no changes, or `nil` if the `itemID` does not exist
+     */
+    public func hasChanges(itemID: NSManagedObjectID) -> Bool? {
+
+        return self.diffableSnapshot.isReloaded(itemID: itemID)
+    }
+
     /**
      The number of items in all sections in the `ListSnapshot`
      */
@@ -340,7 +362,7 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
         return indices.map { position in
 
             let itemID = itemIDs[position]
-            return ObjectPublisher<O>(objectID: itemID, context: context)
+            return context.objectPublisher(objectID: itemID)
         }
     }
 
@@ -354,10 +376,7 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
 
         let context = self.context!
         let itemIDs = self.diffableSnapshot.itemIdentifiers(inSection: sectionID)
-        return itemIDs.map {
+        return itemIDs.map(context.objectPublisher(objectID:))
-
-            return ObjectPublisher<O>(objectID: $0, context: context)
-        }
     }
 
     /**
@@ -374,7 +393,7 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
         return itemIndices.map { position in
 
             let itemID = itemIDs[position]
-            return ObjectPublisher<O>(objectID: itemID, context: context)
+            return context.objectPublisher(objectID: itemID)
         }
     }
 
@@ -391,7 +410,7 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
         return indices.lazy.map { position in
 
             let itemID = itemIDs[position]
-            return ObjectPublisher<O>(objectID: itemID, context: context)
+            return context.objectPublisher(objectID: itemID)
         }
     }
 
@@ -405,10 +424,7 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
 
         let context = self.context!
         let itemIDs = self.diffableSnapshot.itemIdentifiers(inSection: sectionID)
-        return itemIDs.lazy.map {
+        return itemIDs.lazy.map(context.objectPublisher(objectID:))
-
-            return ObjectPublisher<O>(objectID: $0, context: context)
-        }
     }
 
     /**
@@ -425,7 +441,7 @@ public struct ListSnapshot<O: DynamicObject>: RandomAccessCollection, Hashable {
         return itemIndices.lazy.map { position in
 
             let itemID = itemIDs[position]
-            return ObjectPublisher<O>(objectID: itemID, context: context)
+            return context.objectPublisher(objectID: itemID)
         }
     }
 

Sources/NSManagedObjectContext+CoreStore.swift

@@ -99,7 +99,7 @@ extension NSManagedObjectContext {
 
                 return objectPublisher
             }
-            let objectPublisher = ObjectPublisher<O>(objectID: objectID, context: self)
+            let objectPublisher = ObjectPublisher<O>.createUncached(objectID: objectID, context: self)
             cache.setObject(objectPublisher, forKey: objectID)
             return objectPublisher
         }

Sources/ObjectPublisher.swift

@@ -130,7 +130,7 @@ public final class ObjectPublisher<O: DynamicObject>: ObjectRepresentation, Hash
             
             return self
         }
-        return Self.init(objectID: self.id, context: context)
+        return context.objectPublisher(objectID: self.id)
     }
 
     public func asReadOnly(in dataStack: DataStack) -> O? {
@@ -184,9 +184,9 @@ public final class ObjectPublisher<O: DynamicObject>: ObjectRepresentation, Hash
 
     // MARK: Internal
 
-    internal convenience init(objectID: O.ObjectID, context: NSManagedObjectContext) {
+    internal static func createUncached(objectID: O.ObjectID, context: NSManagedObjectContext) -> ObjectPublisher<O> {
 
-        self.init(
+        return self.init(
             objectID: objectID,
             context: context,
             initializer: ObjectSnapshot<O>.init(objectID:context:)

Sources/ObjectRepresentation.swift

@@ -98,7 +98,7 @@ extension DynamicObject where Self: ObjectRepresentation {
     public func asPublisher(in dataStack: DataStack) -> ObjectPublisher<Self> {
 
         let context = dataStack.unsafeContext()
-        return ObjectPublisher<Self>(objectID: self.cs_id(), context: context)
+        return context.objectPublisher(objectID: self.cs_id())
     }
 
     public func asReadOnly(in dataStack: DataStack) -> Self? {

Sources/ObjectSnapshot.swift

@@ -62,7 +62,7 @@ public struct ObjectSnapshot<O: DynamicObject>: ObjectRepresentation, Hashable {
     public func asPublisher(in dataStack: DataStack) -> ObjectPublisher<O> {
         
         let context = dataStack.unsafeContext()
-        return ObjectPublisher<O>(objectID: self.id, context: context)
+        return context.objectPublisher(objectID: self.id)
     }
 
     public func asReadOnly(in dataStack: DataStack) -> O? {