上更新現有記錄

Question

在我ASP.NET-Core Code First project實體框架核心錯誤，我發現了以下錯誤上SaveChangesAsync()在以下Action Method：

錯誤

DbUpdateConcurrencyException: Database operation expected to affect 1 row(s) but actually affected 0 row(s). Data may have been modified or deleted since entities were loaded 

操作方法：

public async Task<IActionResult> UpdateWeekDay(int iWeekDay) 
{ 
     if (ModelState.IsValid) 
     { 
      WeekModel oWeekModel = new WeekModel(); 
      oWeekModel.DayOfWeek= iWeekDay; 
      _context.Update(oWeekModel); 
      await _context.SaveChangesAsync(); 
      return View(); 
     } 
} 

型號：

public class WeekModel 
{ 
    [Key] 
    public int WeekId { get; set; } 
    public int DayOfWeek { get; set; } 
} 

注意：在SQL Server 2014塊都有WeekId as an identity column and as the PK在相應的表格Weeks。而且，該表只包含一條記錄。

UPDATE：

在此之後Post from user sstan，我試圖在上面操作方法如下。它沒有給我一個錯誤，但沒有更新的數據庫，以及：

WeekModel oWeekModel = new WeekModel(); 
_context.WeekModel.Attach(oWeekModel); 
oWeekModel.DayOfWeek= iWeekDay; 
await _context.SaveChangesAsync(); 

Answer 1

在從@Tseng和@ademcaglin和this post from @sstan我能解決這個問題如下建議。 注意：幸得上述用戶（我感謝這些用戶）：

public async Task<IActionResult> UpdateWeekDay(int iWeekDay) 
{ 
    if (ModelState.IsValid) 
    { 
     WeekModel oWeekModel = _context.WeekModel.Where(s => s.DayOfWeek > 0).FirstOrDefault<CurrentYear>(); 
     _context.WeekModel.Attach(oWeekModel); 
     oWeekModel.DayOfWeek= iWeekDay; 
     await _context.SaveChangesAsync(); 
     return View(); 
    } 
}