LINQ to XML查询返回错误的数据

本文关键字：错误 数据 返回 查询 to XML LINQ | 更新日期: 2023-09-27 18:27:50

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到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();

我的问题是我在名单上只得到一个房间，但我应该得到两个。如果这是使用LINQ to xml的正确方式，也请提供建议，我对LINQ还很陌生。

LINQ to XML查询返回错误的数据

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，你将有两个房间。

为什么你的代码不起作用？

  1. select el.Element("Section")只选择Department中的第一个section元素-您永远无法使用id == "001002"从section获得空间
  2. rooms查询中的select el.Element("Room")只返回每个匹配分区中的第一个房间

您可以将Element更改为Elements，并添加额外的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();

作为其他答案的替代方案，您可以使用Extensions.XPathSelectElements方法（XNode，String）（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();

这是你自己的喜好。我发现这本书写起来更短，读起来更容易。

只是为了表明有很多方法可以剥猫的皮：

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();

如果您更改：

select el.Element("Room");

至

select el.Elements("Room");

您只在中间查询中选择一个房间，它应该是.Elements(...)（注意后面的s）：

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

这同样适用于section查询。

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