EF Core - SaveChanges 上没有数据库更新

Question

today I've got a little surprised that my SaveChanges() method of DbContext didn't work as expected.

Here is the method I used to get user data from Db:

        public async Task<UserModel> GetUserByIdAsync(string Id, bool editMode)
        {
            if (editMode) return await UserDbContext.Users.FirstOrDefaultAsync(usr => usr.UserId == Id);
            else return await UserDbContext.Users.AsNoTracking().FirstOrDefaultAsync(usr => usr.UserId == Id);
        }

And here is the method that was supposed to update the entity in Db:

        public async Task<bool> UpdateUserDataByAsync(UserModel updatedUser, ClaimsPrincipal currentUser)
        {
            var user = await GetUserByIdAsync(updatedUser.UserId, true);
            user = updatedUser;
            return await UserDbContext.SaveChangesByAsync(currentUser) > 0;
        }

Also SaveChangesByAsync method is just overriden SaveChanges() to automatically update some Db columns like UpdatedBy :

public async Task<int> SaveChangesByAsync(ClaimsPrincipal userPrincipal,
                                         CancellationToken cancellationToken = new CancellationToken())
        {
            try
            {
                DateTime now = DateTime.UtcNow;
                var entries = ChangeTracker
                    .Entries()
                    .Where(e => e.Entity is BaseModel && (
                            e.State == EntityState.Added
                            || e.State == EntityState.Modified));

                foreach (var entityEntry in entries)
                {
                    ((BaseModel)entityEntry.Entity).UpdatedDate = now;
                    ((BaseModel)entityEntry.Entity).UpdatedBy = userPrincipal.FindFirstValue("UserId") ?? "Anonymous";

                    if (entityEntry.State == EntityState.Added)
                    {
                        ((BaseModel)entityEntry.Entity).CreatedDate = now;
                        ((BaseModel)entityEntry.Entity).CreatedBy = userPrincipal.FindFirstValue("UserId") ?? "Anonymous";
                    }
                }

                return await base.SaveChangesAsync(cancellationToken);
            }
            catch (TaskCanceledException)
            {
                return await Task.FromCanceled<int>(cancellationToken);
            }

        }

Eventually I overcame this problem by changing UpdateUserDataByAsync to the following content:

            UserDbContext.Entry(await GetUserByIdAsync(updatedUser.UserId, true)).CurrentValues.SetValues(updatedUser);
            return await UserDbContext.SaveChangesByAsync(currentUser) > 0;

But I would like to ask you why the initial version didn't work? Since the user was pulled without AsNoTracking() modifier, shouldn't the context keep tracking any change, which in this case was a simple replacement of user data with updatedUser data?

Thank you!

Answer 1

You can make your code much simplier:

public async Task<bool> UpdateUserDataByAsync(UserModel updatedUser, ClaimsPrincipal currentUser)
        {
 UserDbContext.Entry(updatedUser).State = EntityState.Modified;
 return await UserDbContext.SaveChangesByAsync(currentUser) > 0;
}