C#中的LINQ to XML：如何联接XML数据

Question

假设有两个如下所示的XML文件：

<Customers>
  <Customer CustomerID="alc">Alice</Customer>
</Customer>

并且

<Orders>
  <Order OrderID="001" CID="alc">apple</Order>
</Orders>

现在我需要将这两个 XML 文件合并，并使用内连接创建一个新的文件：

<Result>
  <Join>
     <Customer CustomerID="alc">Alice</Customer>
     <Order OrderID="001" CID="alc">apple</Order>
  </Join>
</Result>

我有一个查询：

var result = new XElement("Result",
     from customer in XElement.Load("Customers.xml").Elements("Customer")
        join order in XElement.Load("Orders.xml").Elements("Order")
        on
            (string)customer.Attribute("CustomerID")
        equals
            (string)order.Attribute("CID")
        select new XElement("Join",
               new XElement("Customer", (string)customer.Element("Customer"),
               new XAttribute("CustomerID", (string)customer.Attribute("CustomerID"))),

               new XElement("Order", (string)order.Element("Order"),
               new XAttribute("OrderID", (string)order.Attribute("OrderID")),
               new XAttribute("CID", (string)order.Attribute("CID")))));
result.Save("result.xml");

用这个方法，我无法获取到数据"Alice"和"apple"。结果如下：

<Result>
  <Join>
    <Customer CustomerID="alc" />
    <Order OrderID="001" CID="alc" />
  </Join>
</Result>

我认为(string)customer.Element("Customer")和(string)order.Element("Order")可能存在问题，但我不知道如何修改。

- S.C

Answer 1

你可以将一个元素转换为字符串，以获取它的文本值：

    select new XElement("Join",
           new XElement("Customer", (string)customer,
           new XAttribute("CustomerID", (string)customer.Attribute("CustomerID"))),

           new XElement("Order", (string)order,
           new XAttribute("OrderID", (string)order.Attribute("OrderID")),
           new XAttribute("CID", (string)order.Attribute("CID")))));

- Glorfindel

Answer 2

您可以在创建 Join 元素时简单地传递 customer 和 order 变量，而不是为其创建新的 XElement。

select new XElement("Join", customer, order);

工作演示示例 :

var customersxml = @"<Customers>
  <Customer CustomerID='alc'>Alice</Customer>
</Customers>";
var ordersxml = @"<Orders>
<Order OrderID='001' CID='alc'>apple</Order>
</Orders>";

var result = new XElement("Result",
                          from customer in XElement.Parse(customersxml).Elements("Customer")
                          join order in XElement.Parse(ordersxml).Elements("Order")
                          on (string)customer.Attribute("CustomerID") equals (string)order.Attribute("CID")
                          select new XElement("Join", customer, order));
Console.WriteLine(result.ToString());

output :

<Result>
  <Join>
    <Customer CustomerID="alc">Alice</Customer>
    <Order OrderID="001" CID="alc">apple</Order>
  </Join>
</Result>

- har07