using System;

using System.Collections.Generic;

using System.Linq;

​

//https://stackoverflow.com/questions/76516977/optimizing-a-foreach-or-maybe-transform-it-into-linq

​

using System.Text.Json;

​

public class Student

{

    public string studentName {get; set;}

    public int idCourse {get; set;}

}

​

public class Course

{

    public int id {get; set;}

    public string courseName {get; set;}

    public ICollection<Student> Students {get; set;} = new List<Student>();

}

​

public class CourseDTO

{

    public string courseNameDTO {get; set;}

    public List<string> StudentsFromDTO {get; set;}

}

​

public static class CollectionHelpers

{

    //https://stackoverflow.com/questions/1474863/addrange-to-a-collection

    public static void AddRange<T>(this ICollection<T> destination,

                                   IEnumerable<T> source)

    {

        foreach (T item in source)

        {

            destination.Add(item);

        }

    }

}

​

public class CourseFactory

{

    public static Course FromDTO(CourseDTO dto)

    {

        // How is Course.id set?

        Course createdCourse = new () { courseName = dto.courseNameDTO };

        createdCourse.Students.AddRange(dto.StudentsFromDTO.Select(name => new Student { idCourse = createdCourse.id, studentName = name }));

        return createdCourse;

    }

}

​

public class Program

{

    public static void Main()

    {

        var dto = new CourseDTO

        {

            courseNameDTO = "course name dto",

            StudentsFromDTO = new()

            {

                "Alice",

                "Bob",

            },

        };

        var course = CourseFactory.FromDTO(dto);

        Console.WriteLine("Created {0}:", course);

        Console.WriteLine(JsonSerializer.Serialize(course, new JsonSerializerOptions { WriteIndented = true }));

    }

}