LINQ to XML查詢返回錯誤數據

Question

我有這個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>  

這是我使用Linq to Xml的代碼

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();

我的問題是列表中只有1個房間，但我應該有2個房間。還請告知這是否是使用LINQ到xml的正確方法，我對LINQ還是很陌生。

Answer 1

將sections和rooms查詢更改為：

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");

有了這些，您將獲得2個房間。

為什么您的代碼不起作用？

1. select el.Element("Section")只選擇第一section中的元素Department -你永遠無法從獲得的房間section與id == "001002"
2. 在rooms查詢中select el.Element("Room")在每個匹配部分中僅返回第一個房間。

您可以將Element更改為Elements並添加其他SelectMany(x => x)調用，以使基於語法的查詢正常工作：

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

作為其他答案的替代方法 ，您可以使用Extensions.XPathSelectElements方法（XNode，字符串） （確保將using System.Xml.XPath指令添加到文件頂部）：

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();

這是自己的偏好問題。 我發現這寫起來更短，更容易閱讀。

Answer 3

只是為了證明有很多方法可以給貓皮：

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

您只在中間查詢中選擇一個房間，它應該是.Elements(...) （請注意結尾的s ）：

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

這同樣適用於您的section查詢。