LINQ to XML查询返回错误数据

Question

我有这个XML

<?xml version="1.0" encoding="utf-8" ?>
<Departments>
 <Department>
  <id>001</id>
  <Section>
    <SectionId>001001</SectionId>
    <Room>
      <RoomID>001001001</RoomID>
      <Owner>guest1</Owner>
    </Room>
    <Room>
      <RoomID>001001002</RoomID>
      <Owner>guest11</Owner>
    </Room>
  </Section>
  <Section>
    <SectionId>001002</SectionId>
    <Room>
      <RoomID>001002001</RoomID>
      <Owner>guest2</Owner>
    </Room>
 </Section>
</Department>
</Departments>  

这是我使用Linq to Xml的代码

var xDoc = XDocument.Load(inputUrl);

var sections = from el in xDoc.Descendants("Department")
                       where el.Element("id").Value.Equals("001")
                       select el.Element("Section");

var rooms = from el in sections
               where el.Element("SectionId").Value.Equals("001001")
               select el.Element("Room");

var roomsList = (from el in rooms
            select new Room
            {
                roomID = (string)el.Element("RoomID"),
                owner = (string)el.Element("Owner")
            }).ToList();

我的问题是列表中只有1个房间，但我应该有2个房间。还请告知这是否是使用LINQ到xml的正确方法，我对LINQ还是很陌生。

Answer 1

将sections和rooms查询更改为：

var sections = xDoc.Descendants("Department")
                   .FirstOrDefault(x => (string)x.Element("id") == "001")
                   .Elements("Section");

var rooms = sections.Where(x => (string)x.Element("SectionId") == "001001")
                    .Elements("Room");

有了这些，您将获得2个房间。

为什么您的代码不起作用？

1. select el.Element("Section")只选择第一section中的元素Department -你永远无法从获得的房间section与id == "001002"
2. 在rooms查询中select el.Element("Room")在每个匹配部分中仅返回第一个房间。

您可以将Element更改为Elements并添加其他SelectMany(x => x)调用，以使基于语法的查询正常工作：

var sections = from el in xDoc.Descendants("Department")
                where el.Element("id").Value.Equals("001")
                select el.Elements("Section");

var rooms = from el in sections.SelectMany(x => x)
            where el.Element("SectionId").Value.Equals("001001")
            select el.Elements("Room");

var roomsList = (from el in rooms.SelectMany(x => x)
                    select new 
                    {
                        roomID = (string)el.Element("RoomID"),
                        owner = (string)el.Element("Owner")
                    }).ToList();

Answer 2

作为其他答案的替代方法 ，您可以使用Extensions.XPathSelectElements方法（XNode，字符串） （确保将using System.Xml.XPath指令添加到文件顶部）：

string 
    departmentId = "001", 
    sectionId = "001001";
var xDoc = XDocument.Load(inputUrl);
var rooms = xDoc.XPathSelectElements(
    String.Format(
        "//Department[id={0}]/Section[SectionId={1}]/Room",
        departmentId,
        sectionId))
    .Select(el => new Room
    {
        roomID = (string)el.Element("RoomID"),
        owner = (string)el.Element("Owner")
    }).ToList();

这是自己的偏好问题。 我发现这写起来更短，更容易阅读。

Answer 3

只是为了证明有很多方法可以给猫皮：

var xDoc = XDocument.Load(@"C:\TEST\TEST.XML");

var depts = from e in xDoc.Descendants("Department")
            where e.Element("id").Value.Equals("001")
            select e;

var sections = from e in depts.Descendants("Section")
            where e.Element("SectionId").Value.Equals("001001")
            select e;

var rooms = (from e in sections.Descendants("Room")
            select new //Room 
            {
                ID = (string)e.Element("RoomID"),
                Owner = (string)e.Element("Owner")
            }).ToList();

Answer 4

如果您更改：

select el.Element("Room");

至

select el.Elements("Room");

Answer 5

您只在中间查询中选择一个房间，它应该是.Elements(...) （请注意结尾的s ）：

        var rooms = from el in sections
                       where el.Element("SectionId").Value.Equals("001001")
                       select el.Elements("Room");

这同样适用于您的section查询。