好吧，坦率地说，我没有得到您的算法，但是对于open DataReader问题，请尝试以下代码:

Well, to be frank I don't get your algo but as for open DataReader issue try this code:

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();