我能使用让LINQ加入 - C＃ [英] Can i use join with let in linq - c#

问题描述

let order= _relationContext.Orders 
             .Where(x => x.OrderNumber == orderNo)
             .Select(x => new { x.OrderNo, x.OrderDate }).Single()

我想尝试做这样的事情

let order = _relationContext.Orders join _relationContext.Products 
                     .Where(x => x.OrderNumber == orderNo && x.ProductId == Products.ProductID)
                     .Select(x => new { x.OrderNo, x.OrderDate }).Single()

这甚至可能

更新1：
我当前的代码

UPDATE 1: My current code

    var q = from c in sXDocument.Descendants("prop")
        let handle = c.Element("handle")
        let resultref = handle != null ? handle.Element("dsref") : null
        let orderno = (string)c.Element("orderno")
        let orderdetail = _relationContext.Order 
                        .Where(x => x.orderno == orderno)
                        .Select(x => new { x.ProductID, x.OrderDate }).Single()

        select new Order()
        {
            OrderNo = orderno,
            Handle = resultref != null ? (string)resultref.Attribute("handle") : null,
            Title = //Need ProductName,

            ProductID = orderdetail.ProductID.ToString(),
        };

return q.ToList();

我想，如果我可以使用let关键字的联接，这样我就能拿到产品名称

I figured that if I could use a join in let keyword so I could get the product name

推荐答案

您只能用让作为查询表达式的一部分。如果你要定义一个独立的变量，只是声明它以正常的方式。如果你可以给我们你想要做什么，这将真正帮助更多的什么主意。

You can only use "let" as part of a query expression. If you want to define a separate variable, just declare it in the normal way. If you could give us more idea of what you're trying to do, that would really help.

编辑：您的可以的使用加盟内的让的条款，但只有当它里面一个完整的查询表达式：

You can use "join" within a "let" clause, but only if it's a full query expression inside:

from foo in foos
let bar = (from x in baz join y in qux on x.Id equals y.Id select ...)
select ...

你确定你不应该使用加入让利，而不是开始吗？

Are you sure you shouldn't be using a join instead of a let to start with?

这篇关于我能使用让LINQ加入 - C＃的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！