如何計算表中特定列的總數

Question

我正在計數合計金額重量在某一列中。

我試過下面的代碼，但我似乎只得到第一行的值，而不是其餘。

int QuoteId = (from x in db.Quotes where x.Id != null orderby x.Id descending select x.Id).Take(1).SingleOrDefault(); 
var item = db.QuoteItems.Where(x => x.QuoteId == QuoteId).First(); 
QuoteItemSectionGroup quoteItemList = new QuoteItemSectionGroup(); 
foreach (var quoteItem in db.QuoteItemSectionGroups.Where(x => x.QuoteItemId == item.Id).ToList()) 
{ 
    var total = new QuoteItemSectionGroup 
    { 
     Weight = quoteItem.Weight 
    }; 
    quoteItemList.Weight = total.Weight; 
} 

所以我的問題是：我怎麼能算重量柱總量在我的表？

Answer 1

您顯然想要將當前編號添加到已獲得的Weigth，不是嗎？此外，您不需要創建QuoteItemSectionGroup的新實例，僅僅是爲了臨時設置其Weight屬性。

foreach (var quoteItem in db.QuoteItemSectionGroups.Where(x => x.QuoteItemId == item.Id).ToList()) 
{ 
    quoteItemList.Weight += quoteItem.Weight; // pay attention on the + before the equality-character 
} 

+=的操作者在x += 1是簡單地爲x = x + 1的快捷方式。

或者也可以簡單使用LINQ Sum - 方法

var totalWeight = db.QuoteItemSectionGroups 
    .Where(x => x.QuoteItemId == item.Id) 
    .Sum(x => x.Weight); 

編輯：此外，你還可以簡化你的代碼了一點，所以它終於變成這樣：

var item = db.Quotes.Where(x => x.Id != null) 
    .OrderByDescending(x => x.Id) 
    .FirstOrDefault(); 
var totalWeight = db.QuoteItemSectionGroups 
    .Where(x => x.QuoteItemId == item.Id) 
    .Sum(x => x.Weight);