如何在 EntityFramework 中计算行而不加载内容？

我正在尝试确定如何count使用 EntityFramework 匹配表中的行。

问题是每行可能有很多兆字节的数据（在二进制字段中）。当然，SQL 会是这样的：

SELECT COUNT(*) FROM [MyTable] WHERE [fkID] = '1';

我可以加载所有行并且then找到计数：

var owner = context.MyContainer.Where(t => t.ID == '1');
owner.MyTable.Load();
var count = owner.MyTable.Count();

但这是非常低效的。有没有更简单的方法？

编辑：谢谢大家。我已将数据库从私有附加中移出，以便我可以运行分析；这有帮助，但会引起我意想不到的混乱。

我的真实数据更深一点，我会使用Trucks携带Pallets of Cases of Items——而且我不想要Truck离开，除非至少有一个Item in it.

我的尝试如下所示。我不明白的部分是 CASE_2 从不访问数据库服务器（MSSQL）。

var truck = context.Truck.FirstOrDefault(t => (t.ID == truckID));
if (truck == null)
    return "Invalid Truck ID: " + truckID;
var dlist = from t in ve.Truck
    where t.ID == truckID
    select t.Driver;
if (dlist.Count() == 0)
    return "No Driver for this Truck";

var plist = from t in ve.Truck where t.ID == truckID
    from r in t.Pallet select r;
if (plist.Count() == 0)
    return "No Pallets are in this Truck";
#if CASE_1
/// This works fine (using 'plist'):
var list1 = from r in plist
    from c in r.Case
    from i in c.Item
    select i;
if (list1.Count() == 0)
    return "No Items are in the Truck";
#endif

#if CASE_2
/// This never executes any SQL on the server.
var list2 = from r in truck.Pallet
        from c in r.Case
        from i in c.Item
        select i;
bool ok = (list.Count() > 0);
if (!ok)
    return "No Items are in the Truck";
#endif

#if CASE_3
/// Forced loading also works, as stated in the OP...
bool ok = false;
foreach (var pallet in truck.Pallet) {
    pallet.Case.Load();
    foreach (var kase in pallet.Case) {
        kase.Item.Load();
        var item = kase.Item.FirstOrDefault();
        if (item != null) {
            ok = true;
            break;
        }
    }
    if (ok) break;
}
if (!ok)
    return "No Items are in the Truck";
#endif

CASE_1 产生的 SQL 通过管道传输sp_executesql, but:

SELECT [Project1].[C1] AS [C1]
FROM   ( SELECT cast(1 as bit) AS X ) AS [SingleRowTable1]
LEFT OUTER JOIN  (SELECT 
    [GroupBy1].[A1] AS [C1]
    FROM ( SELECT 
        COUNT(cast(1 as bit)) AS [A1]
        FROM   [dbo].[PalletTruckMap] AS [Extent1]
        INNER JOIN [dbo].[PalletCaseMap] AS [Extent2] ON [Extent1].[PalletID] = [Extent2].[PalletID]
        INNER JOIN [dbo].[Item] AS [Extent3] ON [Extent2].[CaseID] = [Extent3].[CaseID]
        WHERE [Extent1].[TruckID] = '....'
    )  AS [GroupBy1] ) AS [Project1] ON 1 = 1

[我实际上没有卡车、司机、托盘、箱子或物品；正如您从 SQL 中看到的，卡车-托盘和托盘-箱关系是多对多的——尽管我认为这并不重要。我的真实物体是无形的，很难描述，所以我改变了名字。]

查询语法：

var count = (from o in context.MyContainer
             where o.ID == '1'
             from t in o.MyTable
             select t).Count();

方法语法：

var count = context.MyContainer
            .Where(o => o.ID == '1')
            .SelectMany(o => o.MyTable)
            .Count()

两者都会生成相同的 SQL 查询。