Stop user updates from orphaning permission and preference rows (#17645)

* Stop user updates from orphaning permission and preference rows

* Make UserId non-nullable

* Remove unnecessary ToList

* Update Jellyfin.Server.Implementations/Users/UserManager.cs

Co-authored-by: Claus Vium <cvium@users.noreply.github.com>

---------

Co-authored-by: Claus Vium <cvium@users.noreply.github.com>

Jellyfin.Server.Implementations/Users/UserManager.cs

@@ -225,19 +225,8 @@ namespace Jellyfin.Server.Implementations.Users
                         ?? throw new ResourceNotFoundException(nameof(user.Id));
 
                     dbContext.Entry(dbUser).CurrentValues.SetValues(user);
-                    dbContext.Permissions.RemoveRange(dbUser.Permissions);
-                    dbUser.Permissions.Clear();
-                    foreach (var permission in user.Permissions)
-                    {
-                        dbUser.Permissions.Add(new Permission(permission.Kind, permission.Value));
-                    }
-
-                    dbContext.Preferences.RemoveRange(dbUser.Preferences);
-                    dbUser.Preferences.Clear();
-                    foreach (var preference in user.Preferences)
-                    {
-                        dbUser.Preferences.Add(new Preference(preference.Kind, preference.Value));
-                    }
+                    SyncPermissions(dbUser, user.Permissions);
+                    SyncPreferences(dbUser, user.Preferences);
 
                     dbUser.AccessSchedules.Clear();
                     foreach (var accessSchedule in user.AccessSchedules)
@@ -271,6 +260,60 @@ namespace Jellyfin.Server.Implementations.Users
             }
         }
 
+        private static void SyncPermissions(User dbUser, ICollection<Permission> source)
+        {
+            var incoming = new Dictionary<PermissionKind, bool>();
+            foreach (var permission in source)
+            {
+                incoming[permission.Kind] = permission.Value;
+            }
+
+            foreach (var existing in dbUser.Permissions)
+            {
+                if (incoming.Remove(existing.Kind, out var value))
+                {
+                    // EF only marks the row modified if the value actually differs, so an update that
+                    // touches nothing but the user row - a session activity stamp - writes no children.
+                    existing.Value = value;
+                }
+                else
+                {
+                    dbUser.Permissions.Remove(existing);
+                }
+            }
+
+            foreach (var (kind, value) in incoming)
+            {
+                dbUser.Permissions.Add(new Permission(kind, value));
+            }
+        }
+
+        private static void SyncPreferences(User dbUser, ICollection<Preference> source)
+        {
+            var incoming = new Dictionary<PreferenceKind, string>();
+            foreach (var preference in source)
+            {
+                incoming[preference.Kind] = preference.Value;
+            }
+
+            foreach (var existing in dbUser.Preferences)
+            {
+                if (incoming.Remove(existing.Kind, out var value))
+                {
+                    existing.Value = value;
+                }
+                else
+                {
+                    dbUser.Preferences.Remove(existing);
+                }
+            }
+
+            foreach (var (kind, value) in incoming)
+            {
+                dbUser.Preferences.Add(new Preference(kind, value));
+            }
+        }
+
         internal async Task<User> CreateUserInternalAsync(string name, JellyfinDbContext dbContext)
         {
             // TODO: Remove after user item data is migrated.