Question

this is my sample xml.

<Messages>
  <Conversation>
    <id>Z100</id>
    <ReplyToId></ReplyToId>
    <Message>Topic</Message>
  </Conversation>
  <Conversation>
    <id>A100</id>
    <ReplyToId></ReplyToId>
    <Message>This is a test</Message>
  </Conversation>
  <Conversation>
    <id>M100</id>
    <ReplyToId>A100</ReplyToId>
    <Message>What kind of test</Message>
  </Conversation>
  <Conversation>
    <id>A200</id>
    <ReplyToId>M100</ReplyToId>
    <Message>Stage 1</Message>
  </Conversation>
  <Conversation>
    <id>M200</id>
    <ReplyToId>A200</ReplyToId>
    <Message>Test result for </Message>
  </Conversation>
</Messages>

How to get the conversation list based on id using linq in C#. Say for example, If i want to get the conversation for id “A100” which has a link to other conversation based on ReplyToid.

Answer 1

Edit: because of your clarification, I have re-written my answer.

Constructing the Conversation Tree

1. Use XElement to load the root element and its children from your xml file:

   var root = XElement.Load(@"path\to\your.xml"); 
   // Alternatively, XElement.Parse(stringContainingXML);
   

2. Transform the elements into conversations (the conversation class is given below):

   var conversations = (from element in root.Elements()
                        select Conversation.FromXElement(element)).ToList();
   // ToList prevents multiple iteration of the IEnumerable
   

3. Add the replies to each conversation:

   foreach (var conversation in conversations)
   {
       conversation.Replies.AddRange( 
       conversations.Where(reply => reply.ReplyToId == conversation.Id));
   }
   

4. Optionally, remove the replies from the top level:

   conversations.RemoveAll(x => !string.IsNullOrEmpty(x.ReplyToId));
   

5. Optionally, to retrieve a single conversation by id:

   Conversation singleConversation = conversations.Single(x => x.Id == "A100");
   

---

Result

Z100: Topic
A100: This is a test
*->M100: What kind of test
   *->A200: Stage 1
      *->M200: Test result for

---

Conversation Helper Class

public class Conversation
{
    public string Id { get; private set; }
    public string ReplyToId { get; private set; }
    public string Message { get; private set; }
    public readonly List<Conversation> Replies = new List<Conversation>();

    public static Conversation FromXElement(XElement source)
    {
        return new Conversation
        {
            Id = (string)source.Element("id"),
            ReplyToId = (string)source.Element("ReplyToId"),
            Message = (string)source.Element("Message")
        };
    }     
}