Using dependency injection in lazy load model properties

Question

Using dependency injection in lazy load model properties

I am currently using a repository template where I have data models behind the repository that return my domain models. I use dependency injection to do all this. My problem: let's say I have a Student domain model that I get from my StudentRepository. A student may have properties on it that I use in some places, but not others, for example, Courses:

public class Student
{
    public int ID { get; private set; }
    public string Name { get; private set; }

    public Student(int id, string name, IEnumberable courses = null)
    {
        ID = id;
        Name = name;
        _courses = courses;
    }

    private IEnumerable<Course> _courses;

    public IEnumerable<Course> Courses()
    {
        if(_courses == null)
        {
            // I need a good way to load the CourseRepository
            _courses = CourseRepository.GetCoursesByStudentID(ID);
        }

        return _courses;
    }
}

So I want to install this type of lazy loading, but I don’t know how I can do it elegantly, and it’s hard for me to understand how I can load the implementation of CourseRepository (or ICourseRepository using DI), where my repository looks like this:

public class CourseRepository : ICourseRepository
{
    private DbContext _db;

    public CourseRepository(DbContext db)
    {
        _db = db;
    }

    public IEnumerable<DomainModels.Course> GetCoursesByStudentID(int studentID)
    {
        return CourseFactory.Build(_db.Courses.Where(c=>c.StudentID == studentID));
    }
}