Save and load many objects in XML file with C#?

Question

I have this Student class and want to save a list of Student (List students) to XML file as well as read them back from the same XML file to a List of Student. Below shows the function doing the job but only with a single Student object? What should I do to make it work with a List instead?

using System;
using System.IO;
using System.Xml.Serialization;
namespace P02_Xml
{
    public class Student
    {
        public int Id { get; set; } = 1;
        public string FirstName { get; set; } = "";
        public string LastName { get; set; } = "";
        public DateTime DateOfBirth { get; set; } = DateTime.Now;
    }
    class Program
    {
        static void Main(string[] args)
        {
            var student = new Student
            {
                Id = 1,
                FirstName = "Nguyen Van",
                LastName = "A",
                DateOfBirth = new DateTime(1990, 12, 30)
            };
            Console.WriteLine("Original object:");
            Print(student);
            Save(student);
            var nva = Load();
            Console.WriteLine("Deserialized object:");
            Print(nva);
            Console.ReadKey();
        }
        static void Print(Student student)
        {
            Console.WriteLine($"Id: {student.Id}\r\nFirst Name: {student.FirstName}\r\nLast Name: {student.LastName}\r\nDate of birth: {student.DateOfBirth.ToShortDateString()}");
        }
        static void Save(Student student)
        {
            using (var stream = File.OpenWrite("data.xml"))
            {
                XmlSerializer serializer = new XmlSerializer(typeof(Student));
                serializer.Serialize(stream, student);
            }
        }
        static Student Load()
        {
            Student student;
            using (var stream = File.OpenRead("data.xml"))
            {
                var serializer = new XmlSerializer(typeof(Student));
                student = serializer.Deserialize(stream) as Student;
            }
            return student;
        }
    }
}

Do you have to use XmlSerializer? Personally I've usually found that to be more trouble than it's worth - whereas using LINQ to XML and including conversion methods to/from XML in the classes themselves (e.g. Student in this case) is pretty straightforward. — Jon Skeet
– Jon Skeet, Commented Jun 1, 2022 at 6:55

Enigmativity · Accepted Answer · 2022-06-01 07:12:47Z

Based on the code that you have the simplest thing is this:

    static void Save(IEnumerable<Student> students)
    {
        using (var stream = File.OpenWrite("data.xml"))
        {
            XmlSerializer serializer = new XmlSerializer(typeof(Student[]));
            serializer.Serialize(stream, students.ToArray());
        }
    }

    static Student[] Load()
    {
        Student[] student;
        using (var stream = File.OpenRead("data.xml"))
        {
            var serializer = new XmlSerializer(typeof(Student[]));
            student = serializer.Deserialize(stream) as Student[];
        }
        return student;
    }

Now you can do this:

var students = new[]
{
    new Student
    {
        Id = 1,
        FirstName = "Nguyen Van",
        LastName = "A",
        DateOfBirth = new DateTime(1990, 12, 30)
    },
    new Student
    {
        Id = 2,
        FirstName = "Fred",
        LastName = "Nerk",
        DateOfBirth = new DateTime(1990, 12, 30)
    }
};

Save(students);

And load & print like this:

        var nva = Load();

        foreach (var student in nva)
            Print(student);

As Jon Skeet says, XmlSerializer is more trouble than it's worth. I tend to do it this way:

public class Student
{
    public int Id { get; set; } = 1;
    public string FirstName { get; set; } = "";
    public string LastName { get; set; } = "";
    public DateTime DateOfBirth { get; set; } = DateTime.Now;

    public static Student[] FromXDocument(string fileName) =>
        Student.FromXDocument(XDocument.Load(fileName));

    public static Student[] FromXDocument(XDocument document) =>
        document
            .Root
            .Elements("Student")
            .Select(element => new Student()
            {
                Id = (int)element.Attribute("Id"),
                FirstName = element.Attribute("FirstName").Value,
                LastName = element.Attribute("LastName").Value,
                DateOfBirth = (DateTime)element.Attribute("DateOfBirth"),
            })
            .ToArray();

    public static XDocument ToXDocument(IEnumerable<Student> students) =>
        new XDocument(
            new XElement(
                "Students",
                students
                    .Select(student =>
                    new XElement(
                        "Student",
                        new XAttribute("Id", student.Id),
                        new XAttribute("FirstName", student.FirstName),
                        new XAttribute("LastName", student.LastName),
                        new XAttribute("DateOfBirth", student.DateOfBirth)))));
}

Then use it like this:

        Student.ToXDocument(students).Save("students.xml");

        var nva = Student.FromXDocument("students.xml");

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