LINQ系列：LINQ to XML操作

　　LINQ to XML操作XML文件的方法，如创建XML文件、添加新的元素到XML文件中、修改XML文件中的元素、删除XML文件中的元素等。

1. 创建XML文件

string xmlFilePath = Server.MapPath("Data/Product.xml");

XDocument doc = new XDocument
(
    new XDeclaration("1.0", "utf-8", "yes"),
    new XElement
    (
        "Products",
        new XElement
        (
            "Product",
            new XAttribute("ID", 1),
            new XElement("ProductName", "LINQ to XML"),
            new XElement("UnitPrice", 10),
            new XElement("Remark", "LINQ to XML操作")
        )
    )
);

// 保存为XML文件
doc.Save(xmlFilePath);

// 显示XML文件内容
Response.Write(doc);
// 设置网页显示的形式为XML文件
Response.ContentType = "text/xml";
Response.End();

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Products>
  <Product ID="1">
    <ProductName>LINQ to XML</ProductName>
    <UnitPrice>10</UnitPrice>
    <Remark>LINQ to XML操作</Remark>
  </Product>
</Products>

XElement xml = new XElement
(
    "Root",
    new XElement("Product",
        new XAttribute("ID", 1)
    )
);

xml.Save(Environment.CurrentDirectory + @"\" + "Product.xml");

<?xml version="1.0" encoding="utf-8"?>
<Root>
  <Product ID="1" />
</Root>

　　根据从数据库中查询的数据结构生成一个XML文件：

using (NorthwindContext context = new NorthwindContext())
{
    var products = from p in context.Products
                    select new
                    {
                        p.ProductID,
                        p.ProductName,
                        p.UnitPrice
                    };

    var xml = new XElement
    (
        "Products",
        from p in products.ToList()
        select new XElement
        (
            "Product",
            new XElement("ProductID", p.ProductID),
            new XElement("ProductName", p.ProductName),
            new XElement("UnitPrice", p.UnitPrice)
        )
    );

    xml.Save(Environment.CurrentDirectory + @"\" + "Products.xml");
}

2. 加载XML文件

XDocument doc = XDocument.Load(Environment.CurrentDirectory + @"\Product.xml");

foreach (XNode node in doc.Nodes())
{
    Console.WriteLine(node.ToString());
}

　　运行输出：

<!--Created by LINQ to XML-->
<Products>
  <Product>
    <ProductID>1</ProductID>
    <ProductName>LINQ to XML</ProductName>
    <UnitPrice>10</UnitPrice>
  </Product>
  <Product>
    <ProductID>2</ProductID>
    <ProductName>LINQ to SQL</ProductName>
    <UnitPrice>20</UnitPrice>
  </Product>
</Products>

XDocument doc = XDocument.Load(Environment.CurrentDirectory + @"\Product.xml");

foreach (XNode node in doc.Nodes().OfType<XElement>())
{
    Console.WriteLine(node.ToString());
}

<Products>
  <Product>
    <ProductID>1</ProductID>
    <ProductName>LINQ to XML</ProductName>
    <UnitPrice>10</UnitPrice>
  </Product>
  <Product>
    <ProductID>2</ProductID>
    <ProductName>LINQ to SQL</ProductName>
    <UnitPrice>20</UnitPrice>
  </Product>
</Products>

XDocument doc = XDocument.Load(Environment.CurrentDirectory + @"\Product.xml");

foreach (XElement element in doc.Elements())
{
    Console.WriteLine(element.ToString());
}

XElement el = XElement.Load(Environment.CurrentDirectory + @"\Product.xml");

foreach (XElement e in el.Elements("Product"))
{
    Console.WriteLine(e.Element("ProductName").Value);
}

XDocument doc = XDocument.Load(Environment.CurrentDirectory + @"\" + "Product.xml");

var query = from p in doc.Descendants("Product")
            where p.Attribute("ID").Value == "1"
            select p;

foreach (var item in query)
{
    Console.WriteLine(item.Element("ProductName").Value);
}

XDocument doc = XDocument.Load(Environment.CurrentDirectory + @"\" + "Product.xml");

var query = from p in doc.Root.Elements("Product")
            select new
            {
                ProductID = p.Element("ProductID").Value,
                ProductName = p.Element("ProductName").Value,
                UnitPrice = p.Element("UnitPrice").Value
            };
foreach (var item in query)
{
    Console.WriteLine("{0}-{1}-{2}", item.ProductID, item.ProductName, item.UnitPrice);
}

3. 添加元素到XML文件

XElement el = XElement.Load(Server.MapPath("Data/Product.xml"));

XElement product = new XElement
(
    "Product",
    new XAttribute("ID", 2),
    new XElement("ProductName", "LINQ to Object"),
    new XElement("UnitPrice", 20m),
    new XElement("Remark", "")
);

el.Add(product);
el.Save(Server.MapPath("Data/Product.xml"));

<?xml version="1.0" encoding="utf-8"?>
<Products>
  <Product ID="1">
    <ProductName>LINQ to XML</ProductName>
    <UnitPrice>10</UnitPrice>
    <Remark>LINQ to XML操作</Remark>
  </Product>
  <Product ID="2">
    <ProductName>LINQ to Object</ProductName>
    <UnitPrice>20</UnitPrice>
    <Remark></Remark>
  </Product>
</Products>

4. 修改XML文件中元素

XElement el = XElement.Load(Server.MapPath("Data/Product.xml"));

IEnumerable<XElement> products = from e in el.Elements("Product")
                                    where e.Attribute("ID").Value == "1"
                                    select e;
if (products.Count() > 0)
{
    XElement product = products.First();
    product.SetAttributeValue("ID", 3);
    product.ReplaceNodes
    (
        new XElement("ProductName", "LINQ to XML Version 2"),
        new XElement("UnitPrice", 30)
    );
}

el.Save(Server.MapPath("Data/Product.xml"));

<?xml version="1.0" encoding="utf-8"?>
<Products>
  <Product ID="3">
    <ProductName>LINQ to XML Version 2</ProductName>
    <UnitPrice>30</UnitPrice>
  </Product>
  <Product ID="2">
    <ProductName>LINQ to Object</ProductName>
    <UnitPrice>20</UnitPrice>
    <Remark></Remark>
  </Product>
</Products>

5. 删除XML文件中的元素

XElement el = XElement.Load(Server.MapPath("Data/Product.xml"));

IEnumerable<XElement> products = from e in el.Elements("Product")
                                    where e.Attribute("ID").Value == "2"
                                    select e;
if (products.Count() > 0)
{
    products.First().Remove();
}

el.Save(Server.MapPath("Data/Product.xml"));

XElement xml = XElement.Load(Environment.CurrentDirectory + @"\" + "Product.xml");
xml.Element("Product").Remove(); // 删除第一个Product子元素
xml.Elements("Product").Remove(); // 删除全部Product子元素

xml.Save(Environment.CurrentDirectory + @"\" + "Product.xml");

xml.SetElementValue("Product", null); // 删除第一个Product子元素

XElement xml = XElement.Load(Environment.CurrentDirectory + @"\" + "Product.xml");
xml.Element("Product").SetElementValue("ProductID", 1); // 修改ProductID子元素
xml.Element("Product").SetElementValue("ProductID", null); // 删除ProductID子元素

6. 将XML文件中属性转换为元素

XElement el = XElement.Load(Server.MapPath("Data/Product.xml"));

IEnumerable<XElement> products = from e in el.Elements("Product")
                                    where e.Attribute("ID").Value == "1"
                                    select e;
if (products.Count() > 0)
{
    XAttribute attr = products.First().FirstAttribute;
    products.First().AddFirst
    (
        new XElement(attr.Name, attr.Value)
    );
    attr.Remove();
}

el.Save(Server.MapPath("Data/Product.xml"));

<?xml version="1.0" encoding="utf-8"?>
<Products>
  <Product>
    <ID>1</ID>
    <ProductName>LINQ to XML</ProductName>
    <UnitPrice>30</UnitPrice>
  </Product>
</Products>

7.XML节点属性

　　1> 添加属性

XElement xml = XElement.Load(Environment.CurrentDirectory + @"\" + "Product.xml");

XElement product=(from p in xml.Elements("Product")
                    select p).First();
product.Add(new XAttribute("ID", 1));

xml.Save(Environment.CurrentDirectory + @"\" + "Product.xml");

　　2> 修改属性

XElement xml = XElement.Load(Environment.CurrentDirectory + @"\" + "Product.xml");

XElement product = (from p in xml.Elements("Product")
                    select p).First();
product.SetAttributeValue("ID", 2);

xml.Save(Environment.CurrentDirectory + @"\" + "Product.xml");

　　3> 删除属性

XElement xml = XElement.Load(Environment.CurrentDirectory + @"\" + "Product.xml");

XElement product = (from p in xml.Elements("Product")
                    select p).First();
product.Attribute("ID").Remove();

xml.Save(Environment.CurrentDirectory + @"\" + "Product.xml");