Question

这是两个表，

amounttbl,   amountId - amountValue
requesttbl   reqId - reqAmount - Rate - soldAmount, amountId

数据：

 amounttbl
 amountId | amountValue
 ---------|------------
        1 | 5000

 requesttbl
 reqId | reqAmount | Rate | soldAmount | amountId
 ------|-----------|------|------------|---------
      1|       2000|    12|           0|       1
      2|        500|    12|           0|       1
      3|       1000|    11|           0|       1
      4|        500|    10|           0|       1
      5|       1000|    10|           0|       1

为此，我准备了一个行动，应该从高利率到低利率卖出5000，这里它将从（1-2-3）卖出总数将是4500，它将保持500。现在应该分发（4＆amp; 5）。首先，它应该为：

4--500/1500 = 0.33,5至1000/1500 = 0.66

4将获得500％的0.33％，5将获得500％的0.66％。

为此，我创建了一个动作，但它有一些问题：

id = 1;
amount = 5000;
var requests = db.request.Where(a => a.amountId== id).OrderBy(a => a.Rate);
foreach(var item in requests)
{
    decimal soldamount = db.request.Where(a => a.amountId== id).Sum(a => a.reqAmount);
    decimal available= amount - soldamount ;
    while (available>= item.reqAmount)
    {
        item.soldAmount= item.reqAmount;
    }
}
db.SaveChanges();

我在这里遇到两个问题，一个问题在foreach：

已经有一个与此命令关联的开放DataReader 必须先关闭。

这是因为：

decimal soldamount = db.request.Where（a =＆gt; a.amountId == id）.Sum（a =＆gt; a.reqAmount）;

而且我不知道如何计算记录4,5，并确定他们的作用。

Answer 1

嗯，说实话，我没有得到你的算法，但至于open DataReader问题，试试这段代码：

id = 1;
amount = 5000;

//Get list of objects from db (assuming db is `DbContext` and request is `IDbSet` stuff)
var requests = db.request.Where(a => a.amountId== id).OrderBy(a => a.Rate).ToList();

//we already have requests with amountId == id in *requests* variable above.
//db.request.Where(a => a.amountId== id).Sum(a => a.reqAmount);

//This does not change during loop, so calculate before hand
var soldamount = requests.Sum(a => a.reqAmount);

decimal available = amount - soldamount;

foreach(var item in requests)
{
    //don't get concept of while here as you are not changing either
    //item.reqAmount not available
    if(available>= item.reqAmount)
    {
        item.soldAmount= item.reqAmount;
    }
}
db.SaveChanges();

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