Linq to XML query joining parent-child lists

I have an xml file with two lists, forming parent-child relations, like this:

<Categories>

<Category id="10000">Category 1</Category>

<Category id="10100">Category 2</Category>

<Category id="10101">Category 3</Category> ...

</Categories>

<Actions>

<Action name="Action 1"><Categories><Category id="10100"/><Category id="10102"/></Categories></Action>

<Action name="Action 2"><Categories><Category id="10101"/><Category id="10103"/></Categories></Action>

...

</Actions>

Each Action has at least one category from master list. I am trying in my query to expand categories in each action with their names from parent category list, so the output structure would be something like this:

class 开发者_StackOverflowAction {

public string ActionName;

public List<Category> Categories;

}

class Category {

public string CategoryName;

public int CategoryId;

}

I am completely lost, please help.

You could first create a List to store unique Category objects you then reference when creating Action objects. Example C# code:

    XDocument doc = XDocument.Load(@"..\..\XMLFile1.xml");
    List<Category> referencedCategories =
        (from cat in doc.Root.Element("Categories").Elements("Category")
         where doc.Root.Element("Actions").Elements("Action").Elements("Categories").Elements("Category").Any(c2 => cat.Attribute("id").Value == c2.Attribute("id").Value)
         select new Category()
         {
             CategoryId = (int)cat.Attribute("id"),
             CategoryName = (string)cat
         }).ToList();

    List<Action> actions =
        (from action in doc.Root.Element("Actions").Elements("Action")
         select new Action()
         {
             ActionName = (string)action.Attribute("name"),
             Categories = (from cat in referencedCategories
                           where action.Element("Categories").Elements("Category").Any(cat2 => (int)cat2.Attribute("id") == cat.CategoryId)
                           select cat).ToList()
         }).ToList();

    foreach (Action action in actions)
    {
        Console.WriteLine("Action {0}:", action.ActionName);
        foreach (Category cat in action.Categories)
        {
            Console.WriteLine("\tId: {0}; Name: {1}", cat.CategoryId, cat.CategoryName);
        }
        Console.WriteLine();
    }

With the XML sample being

<Root>
  <Categories>
    <Category id="10000">Category 1</Category>
    <Category id="10100">Category 2</Category>
    <Category id="10101">Category 3</Category>
    <Category id="10102">Category 4</Category>
    <Category id="10103">Category 5</Category>
  </Categories>

  <Actions>
    <Action name="Action 1">
      <Categories>
        <Category id="10100"/>
        <Category id="10102"/>
      </Categories>
    </Action>
    <Action name="Action 2">
      <Categories>
        <Category id="10101"/>
        <Category id="10103"/>
      </Categories>
    </Action>
  </Actions>

</Root>

that sample outputs

Action Action 1:
        Id: 10100; Name: Category 2
        Id: 10102; Name: Category 4

Action Action 2:
        Id: 10101; Name: Category 3
        Id: 10103; Name: Category 5

If you prefer to use the join clause the code could be changed as follows:

    XDocument doc = XDocument.Load(@"..\..\XMLFile1.xml");
    List<Category> referencedCategories =
        (from cat in doc.Root.Element("Categories").Elements("Category")
         join cat2 in doc.Root.Element("Actions").Elements("Action").Elements("Categories").Elements("Category") on cat.Attribute("id").Value equals cat2.Attribute("id").Value
         select new Category()
         {
             CategoryId = (int)cat.Attribute("id"),
             CategoryName = (string)cat
         }).ToList();

    List<Action> actions =
        (from action in doc.Root.Element("Actions").Elements("Action")
         select new Action()
         {
             ActionName = (string)action.Attribute("name"),
             Categories = (from cat in referencedCategories
                           join cat2 in action.Element("Categories").Elements("Category") on cat.CategoryId equals (int)cat2.Attribute("id") 
                           select cat).ToList()
         }).ToList();