查詢 XDocument 與查詢 XElement 之比較
當您透過 XDocument.Load 載入文件時，您將會注意到您必須撰寫的查詢與透過 XElement.Load 載入時撰寫的查詢稍有不同。
XDocument.Load 和 XElement.Load 之比較
當您透過 XElement.Load，將 XML 文件載入到 XElement 時，XML 樹狀結構根目錄的 XElement 會包含已載入之文件的根項目。不過，當您透過 XDocument.Load，將相同的 XML 文件載入到 XDocument 時，樹狀目錄的根目錄為 XDocument 節點，而已載入之文件的根項目為允許 XDocument 之子系 XElement 節點的項目。LINQ to XML 座標軸會相對於根節點進行運算。
這個第一個範例會使用 Load 載入 XML 樹狀結構。接著，它會針對樹狀結構根目錄的子項目進行查詢。
// Create a simple document and write it to a file
File.WriteAllText("Test.xml", @"<Root>
<Child1>1</Child1>
<Child2>2</Child2>
<Child3>3</Child3>
</Root>");
Console.WriteLine("Querying tree loaded with XElement.Load");
Console.WriteLine("----");
XElement doc = XElement.Load("Test.xml");
IEnumerable<XElement> childList =
from el in doc.Elements()
select el;
foreach (XElement e in childList)
Console.WriteLine(e);
' Create a simple document and write it to a file
File.WriteAllText("Test.xml", "<Root>" + Environment.NewLine + _
" <Child1>1</Child1>" + Environment.NewLine + _
" <Child2>2</Child2>" + Environment.NewLine + _
" <Child3>3</Child3>" + Environment.NewLine + _
"</Root>")
Console.WriteLine("Querying tree loaded with XElement.Load")
Console.WriteLine("----")
Dim doc As XElement = XElement.Load("Test.xml")
Dim childList As IEnumerable(Of XElement) = _
From el In doc.Elements() _
Select el
For Each e As XElement In childList
Console.WriteLine(e)
Next
這個範例預期會產生下列輸出：
Querying tree loaded with XElement.Load
----
<Child1>1</Child1>
<Child2>2</Child2>
<Child3>3</Child3>
下列範例與上述範例幾乎相同，不同處在於會將 XML 樹狀結構載入到 XDocument 而非 XElement。
// Create a simple document and write it to a file
File.WriteAllText("Test.xml", @"<Root>
<Child1>1</Child1>
<Child2>2</Child2>
<Child3>3</Child3>
</Root>");
Console.WriteLine("Querying tree loaded with XDocument.Load");
Console.WriteLine("----");
XDocument doc = XDocument.Load("Test.xml");
IEnumerable<XElement> childList =
from el in doc.Elements()
select el;
foreach (XElement e in childList)
Console.WriteLine(e);
' Create a simple document and write it to a file
File.WriteAllText("Test.xml", "<Root>" + Environment.NewLine + _
" <Child1>1</Child1>" + Environment.NewLine + _
" <Child2>2</Child2>" + Environment.NewLine + _
" <Child3>3</Child3>" + Environment.NewLine + _
"</Root>")
Console.WriteLine("Querying tree loaded with XDocument.Load")
Console.WriteLine("----")
Dim doc As XDocument = XDocument.Load("Test.xml")
Dim childList As IEnumerable(Of XElement) = _
From el In doc.Elements() _
Select el
For Each e As XElement In childList
Console.WriteLine(e)
Next
這個範例會產生下列輸出：
Querying tree loaded with XDocument.Load
----
<Root>
<Child1>1</Child1>
<Child2>2</Child2>
<Child3>3</Child3>
</Root>
請注意，相同的查詢會傳回一個 Root 節點，而非三個子節點。
其中一個處理方法為，在存取座標軸方法之前，先使用 Root 屬性，如下所示：
// Create a simple document and write it to a file
File.WriteAllText("Test.xml", @"<Root>
<Child1>1</Child1>
<Child2>2</Child2>
<Child3>3</Child3>
</Root>");
Console.WriteLine("Querying tree loaded with XDocument.Load");
Console.WriteLine("----");
XDocument doc = XDocument.Load("Test.xml");
IEnumerable<XElement> childList =
from el in doc.Root.Elements()
select el;
foreach (XElement e in childList)
Console.WriteLine(e);
' Create a simple document and write it to a file
File.WriteAllText("Test.xml", "<Root>" + Environment.NewLine + _
" <Child1>1</Child1>" + Environment.NewLine + _
" <Child2>2</Child2>" + Environment.NewLine + _
" <Child3>3</Child3>" + Environment.NewLine + _
"</Root>")
Console.WriteLine("Querying tree loaded with XDocument.Load")
Console.WriteLine("----")
Dim doc As XDocument = XDocument.Load("Test.xml")
Dim childList As IEnumerable(Of XElement) = _
From el In doc.Root.Elements() _
Select el
For Each e As XElement In childList
Console.WriteLine(e)
Next
這個查詢現在會以查詢樹狀結構根目錄 XElement 的相同方式執行。這個範例會產生下列輸出：
Querying tree loaded with XDocument.Load
----
<Child1>1</Child1>
<Child2>2</Child2>
<Child3>3</Child3>