Linq to XML 查询

使用Linq to XML查询是一种方便快捷的方法，用于处理XML文档。Linq to XML提供了一套强大的查询功能，可以轻松地从XML文档中提取所需的数据。下面将介绍如何使用Linq to XML查询，并通过一个案例代码来说明。

xml
  
    
    John Smith
    2019-01-01
  
  
    
    David Johnson
    2018-05-15
  
  
    
    Lisa Brown
    2020-03-10
  

csharp
XDocument doc = XDocument.Load("books.xml");

csharp
var titles = from book in doc.Descendants("book")
             select book.Element("title").Value;

csharp
XElement newBook = new XElement("book",
                                new XElement("title", "《C++编程基础》"),
                                new XElement("author", "Michael Smith"),
                                new XElement("publishDate", "2021-06-20"));
doc.Root.Add(newBook);

csharp
var titles = from book in doc.Descendants("book")
             where book.Element("author").Value == "John Smith"
             select book.Element("title").Value;

csharp
using System;
using System.Linq;
using System.Xml.Linq;
class Program
{
    static void Main()
    {
        XDocument doc = XDocument.Load("books.xml");
        // 查询所有图书的标题
        var titles = from book in doc.Descendants("book")
                     select book.Element("title").Value;
        Console.WriteLine("所有图书的标题：");
        foreach (var title in titles)
        {
            Console.WriteLine(title);
        }
        // 添加一本新书
        XElement newBook = new XElement("book",
                                        new XElement("title", "《C++编程基础》"),
                                        new XElement("author", "Michael Smith"),
                                        new XElement("publishDate", "2021-06-20"));
        doc.Root.Add(newBook);
        // 查询作者为"John Smith"的图书标题
        var johnSmithTitles = from book in doc.Descendants("book")
                              where book.Element("author").Value == "John Smith"
                              select book.Element("title").Value;
        Console.WriteLine("\n作者为\"John Smith\"的图书标题：");
        foreach (var title in johnSmithTitles)
        {
            Console.WriteLine(title);
        }
    }
}