LINQ XML按属性和嵌套元素查询

// 导入命名空间
using System;
using System.Linq;
using System.Xml.Linq;

// 加载XML文档
XDocument xmlDoc = XDocument.Load("data.xml");

// 属性查询
var elementsWithAttribute = from element in xmlDoc.Descendants("Book")
                            where element.Attribute("Category")?.Value == "Fiction"
                            select element;

// 嵌套元素查询
var elementsWithNestedElement = from element in xmlDoc.Descendants("Book")
                                where element.Element("Author")?.Value == "John Doe"
                                select element;

// 输出结果
foreach (var element in elementsWithAttribute)
{
    Console.WriteLine(element);
}

foreach (var element in elementsWithNestedElement)
{
    Console.WriteLine(element);
}