条件输出通过LINQ到XML

Question

下面是我试图使用LINQ to XML来读取XML示例：

<root> 
    <Employee> 
    <Name>Jeff</Name> 
    <Department>Account</Department> 
    </Employee> 
    <Employee> 
    <Name>David</Name> 
    <Department>Finance</Department> 
    </Employee> 
    <Employee> 
    <Name>Neil</Name> 
    <Department>Sales</Department> 
    </Employee> 
    <Employee> 
    <Name>Jason</Name> 
    <Department>Retail</Department> 
    </Employee> 
</root> 

现在，我需要选择Employee元件，其从 “帐户” Department。如果Account中没有，那么我需要从Finance中挑选Employee元素。 我该怎么做？

Answer 1

你可以这样做，它不是最优雅的方式。只需使用||，并采取FirstOrDefault

var result = doc.Root.Descendants("Employee"). 
       Where(x => x.Element("Department").Value == "Account" || x.Element("Department").Value == "Finance"). 
       FirstOrDefault(); 

Answer 2

结合的LINQ和XPath，你可以做这样的：

var document = XDocument.Load("data.xml").Root; 
//Find a Department with a given value and retrieve its Employee parent 
string xPath = "//Department[text() = '{0}']/parent::Employee"; 

//Search for "Account" Department. If nun was found will return null and then 
//search for "Finance" 
var employee = document.XPathSelectElement(string.Format(xPath, "Account")) ?? 
       document.XPathSelectElement(string.Format(xPath, "Finance")); 

如果你不想使用XPath，那么你可以这样做：

var employee = (from item in XDocument.Load("data.xml").Descendants("Employee") 
       let department = item.Element("Department").Value 
       orderby department == "Account" ? 1 : 
         department == "Finance" ? 2 : 3 
       select item).FirstOrDefault(); 

对于这些部门的所有员工：

var employee = (from item in XDocument.Load("data.xml").Descendants("Employee") 
       group item by item.Element("Department").Value into grouping 
       orderby grouping.Key == "Account" ? 1 : 
         grouping.Key == "Finance" ? 2 : 3 
       select grouping.ToList()).FirstOrDefault(); 

Answer 3

正如你可以使用此代码的选项：

var result = XElement.Parse(xml).Descendants("Employee") 
        .GroupBy(x => x.Element("Department").Value) 
        .OrderByDescending(x=>x.Key=="Account") 
        .FirstOrDefault(x => (x.Key == "Account" && x.Count() > 0) || 
              x.Key == "Finance").ToList();