如何獲取[HttpPost]編輯方法中特定字段的數據庫值？

Question

我需要獲取特定字段「Quantity」的HttpPost Edit方法中的數據庫值，以便我可以對其進行一些操作並更新其值。我使用實體框架6.

[HttpPost] 
[ValidateAntiForgeryToken] 
public async Task<ActionResult> EditGoogles([Bind(Include = "ProductID,Name,Code,Quantity,etc)] SalesDetail salesdetail) 
{ 

    if (ModelState.IsValid) 
    { 

    var oldValue = db.Entry(salesdetail).GetDatabaseValues(); 
    //here i want to get the Quantity from database 
     int QtyBefore = ???; 

    db.Entry(salesdetail).State = EntityState.Modified; 
salesdetail.Quantity = //do some operaion with QtyBefore Here and update 
    await db.SaveChangesAsync(); 
    return Json(new { success = true }); 
    } 
    return PartialView("_EditSales", salesdetail); 
} 

Answer 1

你可以這樣說：

if (ModelState.IsValid) 
{ 
    Models.YourTableName oldValue = db.YourTableName.Where(q=>q.Quantity==salesdetail.Quantity).Select(p=>p).SingleOrDefault(); 
    oldValue.Quantity= YourNewValue; 
    ... 

Answer 2

而實際上不必所有必要的信息，這就是我認爲你需要：

[HttpPost] 
[ValidateAntiForgeryToken] 
public async Task<ActionResult> EditGoogles([Bind(Include = "ProductID,Name,Code,Quantity,etc)] SalesDetail salesdetail) 
{ 

    if (ModelState.IsValid) 
    { 

    var oldValue = db.Entry(salesdetail).GetDatabaseValues(); 
    //here i want to get the Quantity from database 
     int QtyBefore = db.Set<SalesDetail>().FirstOrDefault(x => x.Quantity == yourquantityid)?.Quantity ; 

    db.Entry(salesdetail).State = EntityState.Modified; 
salesdetail.Quantity = //do some operaion with QtyBefore Here and update 
    await db.SaveChangesAsync(); 
    return Json(new { success = true }); 
    } 
    return PartialView("_EditSales", salesdetail); 
} 

您還可以找到關於查詢數據庫的文章堆，例如this之一。