XML File I/O

When to Use XML Files

Use XML for hierarchical/nested data structures where records may have variable numbers of child elements. Self-describing and flexible.

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XML File Helper Class

Click to view XmlFileHelper.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Xml.Linq;

public static class XmlFileHelper
{
    // Path constant (recommended for Unit 3)
    private const string XML_PATH = "data/students.xml";

    public static List<StudentResult> LoadFromXml()
    {
        var results = new List<StudentResult>();
        if (!File.Exists(XML_PATH)) return results;

        var doc = XDocument.Load(XML_PATH);

        foreach (var s in doc.Root?.Elements("student") ?? new List<XElement>())
        {
            results.Add(new StudentResult
            {
                StudentID = (int)s.Element("id")!,
                FirstName = (string)s.Element("firstName")!,
                LastName  = (string)s.Element("lastName")!,
                Score     = (int)s.Element("score")!
            });
        }

        return results;
    }

    public static void SaveToXml(List<StudentResult> results)
    {
        var doc = new XDocument(
            new XElement("students",
                results.ConvertAll(r =>
                    new XElement("student",
                        new XElement("id", r.StudentID),
                        new XElement("firstName", r.FirstName),
                        new XElement("lastName", r.LastName),
                        new XElement("score", r.Score)
                    )
                )
            )
        );

        doc.Save(XML_PATH);
    }
}

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Usage Example

using System.Xml.Linq;

// Load the XML file
XDocument doc = XDocument.Load("library.xml");

// Get all book elements
var books = doc.Descendants("book");

// Process each book
foreach (var book in books)
{
    // Extract data using tag names
    string id = book.Attribute("id").Value;
    string title = book.Element("title").Value;
    string year = book.Element("year").Value;

    Console.WriteLine($"Book {id}: {title} ({year})");

    // Handle multiple authors (if present)
    var authors = book.Descendants("author");
    foreach (var author in authors)
    {
        Console.WriteLine($"  Author: {author.Value}");
    }
}

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Example XML File Structure

<?xml version="1.0" encoding="utf-8"?>
<library>
  <book id="101">
    <title>Clean Code</title>
    <author>Robert Martin</author>
    <year>2008</year>
    <categories>
      <category>Programming</category>
      <category>Software Engineering</category>
    </categories>
    <available>true</available>
  </book>

  <book id="102">
    <title>Design Patterns</title>
    <authors>
      <author>Erich Gamma</author>
      <author>Richard Helm</author>
      <author>Ralph Johnson</author>
      <author>John Vlissides</author>
    </authors>
    <year>1994</year>
    <available>false</available>
  </book>
</library>

Advantages of XML

• Can handle variable numbers of child elements (multiple authors)
• Self-describing with tags
• Can handle commas/line breaks in data without breaking structure
• Extensible and flexible