如何根據多個父母的屬性刪除子元素？

Question

我有將類似於下面的結構的XML文件：

<?xml version="1.0" encoding="utf-8"?> 
<Root Attr1="Foo" Name="MyName" Attr2="Bar" > 
    <Parent1 Name="IS"> 
     <Child1 Name="Kronos1"> 
      <GrandChild1 Name="Word_1"/> 
      <GrandChild2 Name="Word_2"/> 
      <GrandChild3 Name="Word_3"/> 
      <GrandChild4 Name="Word_4"/> 
     </Child1> 
     <Child2 Name="Kronos2"> 
      <GrandChild1 Name="Word_1"/> 
      <GrandChild2 Name="Word_2"/> 
      <GrandChild3 Name="Word_3"/> 
      <GrandChild4 Name="Word_4"/> 
     </Child2> 
    </Parent1> 
</Root> 

中的元素不會在定義他們可以具有比其它文件不同的值。我所知道的是每個元素的「名稱」屬性，它總是被定義的。我需要能夠根據該名稱操作和/或刪除選定元素內的數據。例如：removeElement("MyName.IS.Kronos1.Word_1")將刪除Child1父級下的GrandChild1元素。

我的問題是，雖然使用LINQ to XML查詢，我無法正確選擇該元素。使用此：

private IEnumerable<XElement> findElements(IEnumerable<XElement> docElements, string[] names) 
{ 
    // the string[] is an array from the desired element to be removed. 
    // i.e. My.Name.IS ==> array[ "My, "Name", "IS"] 
    IEnumerable<XElement> currentSelection = docElements.Descendants(); 

    foreach (string name in names) 
    { 
     currentSelection = 
      from el in currentSelection 
      where el.Attribute("Name").Value == name 
      select el; 
    } 

    return currentSelection; 

} 

要查找我需要刪除的元素產生這樣的結果：

<?xml version="1.0" encoding="utf-8"?> 
<Root Attr1="Foo" Name="MyName" Attr2="Bar" > 
    <Parent1 Name="IS"> 
     <Child1 Name="Kronos1"> 
      <GrandChild2 Name="Word_2"/> 
      <GrandChild3 Name="Word_3"/> 
      <GrandChild4 Name="Word_4"/> 
     </Child1> 
     <Child2 Name="Kronos2"> 
      <GrandChild2 Name="Word_2"/> 
      <GrandChild3 Name="Word_3"/> 
      <GrandChild4 Name="Word_4"/> 
     </Child2> 
    </Parent1> 
</Root> 

調試看來，我做的是重新搜索同一文檔後，但每次都有不同的名字。如何根據多個父屬性名稱搜索和選擇特定元素？

需要注意的是，XML的大小（即元素的等級）也是可變的。這意味着可以有2層（家長）或6層（偉大 - 大孩子）。但是，我需要能夠查看根節點的Name屬性。

Answer 1

這應該工作：

if (doc.Root.Attribute("Name").Value != names.First()) 
    throw new InvalidOperationException("Sequence contains no matching element."); 

var selection = doc.Root; 

foreach (var next in names.Skip(1)) 
    selection = selection.Elements().First(x => x.Attribute("Name").Value == next); 

return selection; 

您可以通過以下替換最新行，如果你想：

var selection = names.Skip(1).Aggregate(doc.Root, (current, next) => current.Elements().First(x => x.Attribute("Name").Value == next)); 

如果在源中找不到匹配的元素，則.First()方法會引發異常。

---

最乾淨的方法是添加一個新功能：

XElement SelectChildElement(XElement current, string child) 
{ 
    if (current == null) 
     return null;   

    var elements = current.Elements(); 
    return elements.FirstOrDefault(x => x.Attribute("Name").Value == child); 
} 

，這樣你可以簡單地使用它如下：

if (doc.Root.Attribute("Name").Value != names.First()) 
    return null; 

return names.Skip(1).Aggregate(doc.Root, SelectChildElement); 

然後，如果你需要選擇一個孩子，你有一個方便的SelectChildElement() avaialble。如果您想改爲使用myElement.SelectChild(child)，則可以從extension調用它。

另外，當您在此處使用FirstOrDefault時，您不會收到異常，但會返回null。

通過這種方式，它並沒有跟蹤異常的這往往是更昂貴的...

Answer 2

您需要搜索當前所選元素的後代在每個新的一步：

private IEnumerable<XElement> findElements(IEnumerable<XElement> docElements, string[] names) 
{ 
    IEnumerable<XElement> currentSelection = docElements; 
    IEnumerable<XElement> elements = currentSelection; 

    foreach (string name in names) 
    { 
     currentSelection = 
      from el in elements 
      where el.Attribute("Name").Value == name 
      select el; 
     elements = currentSelection.Elements(); 
    } 

    return currentSelection; 
} 

我LinqPad測試下面的代碼和你想要的一切工作。你也可以看到所有的中間步驟。順便說一下，LinqPad是測試你的linq查詢的好工具。

string xml = 
"<?xml version=\"1.0\" encoding=\"utf-8\"?>" + 
"<Root Attr1=\"Foo\" Name=\"MyName\" Attr2=\"Bar\" >" + 
" <Parent1 Name=\"IS\">" + 
"  <Child1 Name=\"Kronos1\">" + 
"   <GrandChild1 Name=\"Word_1\"/>" + 
"   <GrandChild2 Name=\"Word_2\"/>" + 
"   <GrandChild3 Name=\"Word_3\"/>" + 
"   <GrandChild4 Name=\"Word_4\"/>" + 
"  </Child1>" + 
"  <Child2 Name=\"Kronos2\">" + 
"   <GrandChild1 Name=\"Word_1\"/>" + 
"   <GrandChild2 Name=\"Word_2\"/>" + 
"   <GrandChild3 Name=\"Word_3\"/>" + 
"   <GrandChild4 Name=\"Word_4\"/>" + 
"  </Child2>" + 
" </Parent1>" + 
"</Root>"; 

string search = "MyName.IS.Kronos1.Word_1"; 
string[] names = search.Split('.'); 

IEnumerable<XElement> currentSelection = XElement.Parse(xml).AncestorsAndSelf(); 
IEnumerable<XElement> elements = currentSelection; 
currentSelection.Dump(); 

foreach (string name in names) 
{ 
    currentSelection = 
     from el in elements 
     where el.Attribute("Name").Value == name 
     select el; 
    elements = currentSelection.Elements(); 
    currentSelection.Dump(); 
} 

Answer 3

使用這個庫使用XPath：如果你採取遞歸方法可以做到這一點https://github.com/ChuckSavage/XmlLib/

string search = "MyName.IS.Kronos1.Word_1"; 
XElement node, root = node = XElement.Load(file); 
// Skip(1) is to skip the root, because we start there and there can only ever be one root 
foreach (string name in search.Split('.').Skip(1)) 
    node = node.XPathElement("*[@Name={0}]", name); 
node.Remove(); 
root.Save(file); 

Answer 4

：

private XElement findElement(IEnumerable<XElement> docElements, List<string> names) 
{ 


    IEnumerable<XElement> currentElements = docElements; 
    XElement returnElem = null; 
    // WE HAVE TO DO THIS, otherwise we lose the name when we remove it from the list 
    string searchName = String.Copy(names[0]); 

    // look for elements that matchs the first name 
    currentElements = 
     from el in currentElements 
     where el.Attribute("Name").Value == searchName 
     select el; 

    // as long as there's elements in the List AND there are still names to look for: 
    if (currentElements.Any() && names.Count > 1) 
    { 
     // remove the name from the list (we found it above) and recursively look for the next 
     // element in the XML 
     names.Remove(names[0]); 
     returnElem = findElement(currentElements.Elements(), names); 
    } 

    // If we still have elements to look for, AND we're at the last name: 
    else if (currentElements.Any() && names.Count == 1) 
    { 
     // one last search for the final element 
     currentElements = 
     from el in currentElements 
     where el.Attribute("Name").Value == searchName 
     select el; 

     // we return the the first elements which happens to be the only one (if found) or null if not 
     returnElem = currentElements.First(); 
    } 
    else 
     // we do this if we don't find the correct elements 
     returnElem = null; 

    // if we don't find the Element, return null and handle appropriately 
    // otherwise we return the result 
    return returnElem; 
} 

請注意，我傳遞一個列表，而不是數組。這很容易通過以下完成：

List<string> elemNames= new List<string>("This.is.a.test".Split('.')); // or whatever your string is that you need to split 

最後，我讀的文件，它分裂成元素，並調用函數如下：

XDocument doc = XDocument.Load(loadLocation); 
IEnumerable<XElement> currentSelection = doc.Elements(); 
XElement foundElement = findElement(currentSelection, elemNames);