Csharp . NET在上一个操作完成之前，在此上下文实例上启动了第二个操作

我得到了这个错误:"System. InvalidOperationException:'在上一个操作完成之前，在此上下文实例上启动了第二个操作.这通常是由不同线程并发使用同一个DbContext实例造成的.

这是我的服务代码:

public async Task<IQueryable<GetAllUsersDTO>> UsersById(Guid userId, CancellationToken cancellationToken)
{
try
{
    var Log = await _db.Users
                        .Include(x => x.University)
                        .Include(x => x.Fields)
                        .Where(x => x.UserId == userId)
                        .OrderByDescending(x => x.CreatedAt)
                        .AsNoTracking()
                        .ToListAsync();

    var logsDTO = await Task.WhenAll(Log.Select(async x =>
    {
        var userInDb = await _db.Users.FindAsync((Guid)x.UserId); 
        var user = await _userService.GetDirectoryInformation(userInDb, cancellationToken);
        return new GetAllUsersDTO()
        {
            Description = x.Description,
            PostDate = x.PostDate,
            Id = x.Id,
            RecieveUserId = x.RecieveUserId,
            UniversityId = x.UniversityId,
            IsVisible = x.IsVisible,
            IsApproved = x.IsApproved,
            UserIdOpen = x.UserId,
            UserName = user.UserName,
            LogTitle = x.LogTitle,
            LogNr = x.LogNr,
            Email = user.Email,
        };
    }));

    return logsDTO.AsQueryable();
}
catch (Exception ex)
{
    Console.WriteLine("Error=", ex.Message);
    throw;
}
}

这就是我在这个服务中注入DataContext的方式:

private readonly DataContext _db;
public UserService(DataContext context) : base(context)
{
 _db = context;
}

注意:此服务仅在日志(log)列表仅返回一个数据时才起作用.但是当它返回多个数据时，它会触发错误.

我试着用ServiceLifetime.Scoped配置依赖注入设置，结果如下所示:

builder.Services
    .AddDbContext<DataContext>(opt =>
        opt.UseSqlServer(builder.Configuration.GetConnectionString("connString"))
        ,ServiceLifetime.Scoped
    );