LINQ to XML 实战
LINQ to XML 轴
定义:
创建XML树或将XML文档加载到XML树之后,可以进行查询,从而查找元素并检索它们的值。
两类轴方法:
-一些轴就是XELement和XDocument类中返回IEnumerable(T)集合的方法。
-另一些轴方法是Extensions类中的扩展方法。实现为扩展方法的轴对集合进行操作,然后返回集合。
XContainer是XElement的基类!
-常见的轴方法:
-XContainer.Elements()返回集合
-XContainer.Descendants()返回集合
-XContainer.Element()返回单个元素
-XElement.Attribute(XName)返回单个属性
-XElement.Attributes(XName)返回所有属性集合
下面是XElement类(或其基类)的方法汇总,可以对XElement调用这些方法以返回元素集合
-XNode.Ancestors 返回此元素的上级的XElement的IEnumerable(T)
-XContainer.Descendants 返回此元素的子代的XElement的IEnumerable(T)
-XContainer.Elements 返回此元素的子元素XElement的IEnumerable(T)
-XNode.ElementsAfterSelf 返回此元素之后的元素的XElement的IEnumerable(T)
-XNode.ElementsBeforeSelf 返回此元素之前的元素的XElement的IEnumerable(T)
-XElement.AncestorsAndSelf 返回此元素及其上级的XElement的IEnumerable(T)
-XElementDescendantsAndSelf 返回此元素及其子代的XElement的IEnumerable(T)
如何获取元素的值,有两种主要方法可以完成此操作
– 一种方法是将XElement 或XAttribute 强制转换为所需的类型。然后,显式转换运算符将元素或属性的内容转换为指定的类型,并将其分配给变量。
– 此外,还可以使用XElement.Value 属性或XAttribute.Value 属性,但是,对于C#,强制转换通常是更好的方法。在检索可能存在也可能不存在的元素(或属性)的值时,如果将元素或属性强制转换为可以为null 的类型,则代码会更易于编写无法通过强制转换设置元素的内容,而通过XElement.Value 属性可以做到这一点。
实例代码
- XElement root = XElement.Load("PurchaseOrders.xml");
- IEnumerable<XElement> purchaseOrders =
- from el in root.Elements("PurchaseOrder")
- where
- (from add in el.Elements("Address")
- where
- (string)add.Attribute("Type") == "Shipping" &&
- (string)add.Element("State") == "NY"
- select add)
- .Any()
- select el;
- foreach (XElement el in purchaseOrders)
- Console.WriteLine((string)el.Attribute("PurchaseOrderNumber"));
// //筛选可选元素
- XElement root = XElement.Parse(@"<Root>
- <Child1>
- <Text>Child One Text</Text>
- <Type Value=""Yes""/>
- </Child1>
- <Child2>
- <Text>Child Two Text</Text>
- <Type Value=""Yes""/>
- </Child2>
- <Child3>
- <Text>Child Three Text</Text>
- <Type Value=""No""/>
- </Child3>
- <Child4>
- <Text>Child Four Text</Text>
- <Type Value=""Yes""/>
- </Child4>
- <Child5>
- <Text>Child Five Text</Text>
- </Child5>
- </Root>");
- var cList =
- from typeElement in root.Elements().Elements("Type")
- where (string)typeElement.Attribute("Value") == "Yes"
- select (string)typeElement.Parent.Element("Text");
- foreach (string str in cList)
- Console.WriteLine(str);
//对元素进行排序
- XElement root = XElement.Load("Data.xml");
- IEnumerable<decimal> prices =
- from el in root.Elements("Data")
- let price = (decimal)el.Element("Price")
- orderby price
- select price;
- foreach (decimal el in prices)
- Console.WriteLine(el);
////对多个键上的元素进行排序
- XElement co = XElement.Load("CustomersOrders.xml");
- var sortedElements =
- from c in co.Element("Orders").Elements("Order")
- orderby (string)c.Element("ShipInfo").Element("ShipPostalCode"),
- (DateTime)c.Element("OrderDate")
- select new
- {
- CustomerID = (string)c.Element("CustomerID"),
- EmployeeID = (string)c.Element("EmployeeID"),
- ShipPostalCode = (string)c.Element("ShipInfo").Element("ShipPostalCode"),
- OrderDate = (DateTime)c.Element("OrderDate")
- };
- foreach (var r in sortedElements)
- Console.WriteLine("CustomerID:{0} EmployeeID:{1} ShipPostalCode:{2} OrderDate:{3:d}",
- r.CustomerID, r.EmployeeID, r.ShipPostalCode, r.OrderDate);
////计算中间值
- XElement root = XElement.Load("Data.xml");
- IEnumerable<decimal> extensions =
- from el in root.Elements("Data")
- let extension = (decimal)el.Element("Quantity") * (decimal)el.Element("Price")
- where extension >= 25
- orderby extension
- select extension;
- foreach (decimal ex in extensions)
- Console.WriteLine(ex);
//编写基于上下文查找元素的查询
- XElement doc = XElement.Parse(@"<Root>
- <p id=""1""/>
- <ul>abc</ul>
- <Child>
- <p id=""2""/>
- <notul/>
- <p id=""3""/>
- <ul>def</ul>
- <p id=""4""/>
- </Child>
- <Child>
- <p id=""5""/>
- <notul/>
- <p id=""6""/>
- <ul>abc</ul>
- <p id=""7""/>
- </Child>
- </Root>");
- IEnumerable<XElement> items =
- from e in doc.Descendants("p")
- let z = e.ElementsAfterSelf().FirstOrDefault()
- where z != null && z.Name.LocalName == "ul"
- select e;
- foreach (XElement e in items)
- Console.WriteLine("id = {0}", (string)e.Attribute("id"));
////通过 LINQ to XML 使用字典
- Dictionary<string, string> dict = new Dictionary<string, string>();
- dict.Add("Child1", "Value1");
- dict.Add("Child2", "Value2");
- dict.Add("Child3", "Value3");
- dict.Add("Child4", "Value4");
- XElement root = new XElement("Root",
- from keyValue in dict
- select new XElement(keyValue.Key, keyValue.Value)
- );
XElement root = XElement.Load("Data.xml");
- Dictionary<string, string> dict = new Dictionary<string, string>();
- foreach (XElement el in root.Elements())
- dict.Add(el.Name.LocalName, el.Value);
- foreach (string str in dict.Keys)
- Console.WriteLine("{0}:{1}", str, dict[str]);
- Console.WriteLine(root);
/////检索元素的值
- XElement e = new XElement("StringElement", "abcd");
- Console.WriteLine(e);
- Console.WriteLine("Value of e:" + (string)e);
- Console.WriteLine("Value of e by Value:" + e.Value);
//检索元素集合
- XElement po = XElement.Load("PurchaseOrder.xml");
- IEnumerable<XElement> childElements = from el in po.Elements()
- select el;
- foreach (XElement el in childElements)
- Console.WriteLine("Name: " + el.Name);
////根据元素的名称进行筛选
- XElement po = XElement.Load("PurchaseOrder.xml");
- IEnumerable<XElement> items = from el in po.Descendants("ProductName")
- select el;
- foreach (XElement proName in items)
- Console.Write("PrdName" + ":" + (string)proName);
////根据元素的名称进行筛选(有命名空间)
- XNamespace aw = "http://www.adventure-works.com";
- XElement po = XElement.Load("PurchaseOrderInNamespace.xml");
- IEnumerable<XElement> items = from el in po.Descendants(aw + "ProductName")
- select el;
- foreach (XElement prdName in items)
- Console.WriteLine(prdName.Name + ":" + (string)prdName);
////链接轴方法,有时,当可能存在或不存在间隔上级时,您希望在特定的元素深度,检索所有的元素
- XElement root = XElement.Load("Irregular.xml");
- IEnumerable<XElement> configParameters =root.Elements("Customer").Elements("Config").
- Elements("ConfigParameter");
- foreach (XElement cp in configParameters)
- Console.WriteLine(cp.Value);
////检索单个子元素
- XElement po = XElement.Load("PurchaseOrder.xml");
- XElement e = po.Element("DeliveryNotes");
- Console.WriteLine(e);
////检索属性type的值
- XElement val = new XElement("Value",
- new XAttribute("ID", "1243"),
- new XAttribute("Type", "int"),
- new XAttribute("ConvertableTo", "double"),
- "100");
- IEnumerable<XAttribute> xa = from att in val.Attributes()
- select att;
- foreach (XAttribute a in xa)
- if (a.Name.ToString() == "Type")
- Console.WriteLine(a.Value);
XElement cust = new XElement("PhoneNumbers",
- new XElement("Phone",
- new XAttribute("type", "home"),
- "555-555-5555"),
- new XElement("Phone",
- new XAttribute("type", "work"),
- "555-555-6666")
- );
- IEnumerable<XElement> elList = from el in cust.Descendants("Phone")
- select el;
- foreach (XElement el in elList)
- Console.WriteLine((string)el.Attribute("type"));
////查找具有特定属性的元素
- XElement root = XElement.Load("PurchaseOrder.xml");
- IEnumerable<XElement> address = from el in root.Elements("Address")
- where (string)el.Attribute("Type") == "Billing"
- select el;
- foreach (XElement el in address)
- Console.WriteLine(el);
- XElement root = XElement.Load("TestConfig.xml");
- IEnumerable<XElement> tests = from el in root.Elements("Test")
- where (string)el.Element("CommandLine") == "Examp2.EXE"
- select el;
- foreach (XElement el in tests)
- Console.WriteLine((string)el.Attribute("TestId"));