具有相同商品id的商品价格总和

Question

我想在数据库表中具有相同项目id的所有行中的所有项目价格的总和。我的意思是，结果应该是一个数字，当我从下拉列表中选择一个特定的项目id时，它会自动放在文本框中。

我如何在linq中做到这一点？

public double oIlstGetVouchersDetailjh(int nvoucherID)
{
    Training_sNairoukhEntities1 sNairoukhEntities1 = new Training_sNairoukhEntities1();
    double sum = (from Entity in sNairoukhEntities1.INV_InventoryItems
                                where Entity.ItemID == nvoucherID
                                select Entity.ItemPrice).sum();
    return sum;
}

或

public double oIlstGetVouchersDetailjh(int nvoucherID)
{
    Training_sNairoukhEntities1 sNairoukhEntities1 = new Training_sNairoukhEntities1();
    double olstInvoicesSrech = from Entity in sNairoukhEntities1.INV_InventoryItems
    group Entity by Entity.ItemID == nvoucherID into g
    select g.sum(Entity => Entity.ItemPrice);

    return olstInvoicesSrech;
}

但是第二个查询告诉我这个消息不能隐式地将类型'System.Linq.IQueryable‘转换为'double

Answer 1

在您的情况下，这将是可行的：

    Training_sNairoukhEntities1 sNairoukhEntities1 = new Training_sNairoukhEntities1();
    double sum = (from Entity in sNairoukhEntities1.INV_InventoryItems
                                where Entity.ItemID == nvoucherID
                                select Entity.ItemPrice).Sum(); // Change sum to Sum
    return sum;

这里有一个更简单的方法：

sNairoukhEntities1.INV_InventoryItems.Where(item => item.ItemID == nvoucherID).Sum(item => item.ItemPrice);