Question

如何在第二次查询中替换ProductID的值？

var pid= from t in Products where t.Name == "Cable Lock" select  t.ProductID

var f=from k in SalesOrderDetails where k.ProductID= select k;
f.Dump();

Answer 1

尝试

var orderDetails = from o in SalesOrderDetails
                   join p in Products on p.ProductID equals o.ProductID
                   where (p.Name == "Cable Lock")
                   select o;

或使用子查询：

var orderDetails = from o in SalesOrderDetails
                   where Products.Any(p => p.Name == "Cable Lock")
                   select o;

Answer 2

我不确定你为什么不去Joins，但如果我按照你的逻辑，你在代码中遗漏FirstOrDefault，你可以这样做： -

var pid = (from t in products where t.Name == "Cable Lock" select t.ProductID).FirstOrDefault();

然后，您可以在下一个查询中使用此productId： -

var f= from k in SalesOrderDetails where k.ProductId == pid  select k;

Answer 3

您遇到的问题是var pid= from t in Products where t.Name == "Cable Lock" select t.ProductID类型为IQueryable<int>，IEnumerable不是单一值。

所以你可以选择以下其中一个

var pid = (from p in Products
          where p.Name == "Cable Lock"
          select p.Id).Single();
var f = from k in SalesOrderDetails where k.ProductID= select k;

OR

var pid = from p in Products
          where p.Name == "Cable Lock"
          select p.Id;
var f = from k in SalesOrderDetails where pid.Contains(k.ProductID) select k;

如何替换LINQ子查询的值

3 个答案: