Adding Entity with complex type property - entity-framework-core

Question

I am trying to add the student entity in my database, which looks like this:
public class Student
{
public int ID { get; set; }
public string Name { get; set; }
public Course Course { get; set; }
}
The Course class looks like this:
public class Course
{
public int ID { get; set; }
public string Name { get; set; }
}
Data in the Course table:
| ID | Course |
------------------------
| 1 | Math |
-----------------------
| 2 | Physics |
-----------------------
When I define student as shown below:
var student = new Student
{
Name = "ABC",
Course = new Course { ID = 1, Name = "Math"}
};
and try to add it so
context.Students.add(student);
await context.SaveChangesAsync()
the entity wasn't added. I added this line of code
context.Entry(student).State = EntityState.Added;
but nothing changed.

Answer 1

First of all you have to set Foreign Key CourseId to your Student entity.
A) Student Entity
public class Student
{
public int StudentID { get; set; }
public string Name { get; set; }
public int CourseID { get; set; } //This is foreign key
public virtual Course Course { get; set; }
}
B) Course Entity: ICollection property gives you all students with particular CourseID.
public class Course
{
public int CourseID { get; set; }
public string Name { get; set; }
public virtual ICollection<Student> Students { get; set; }
}
1) If you add new student record with new course then
Course course = new Course
{
Name = "Math"
};
Course insertedCourse = context.Courses.Add(course);
Student student = new Student
{
CourseID = insertedCourse.CourseID,
Name = "ABC"
};
context.Students.Add(student);
await context.SaveChangesAsync();
2) If you have to reference your existing course from database then you have to get course from database and assign courseId to student entity.
Course existingCourse = GetCourseByIdFromDatabase();
Student student = new Student
{
CourseID = existingCourse.CourseID, //This ID comes from Db
Name = "ABC"
};
context.Students.Add(student);
await context.SaveChangesAsync();
Try once may it help you.
Edited:
As I understood with your last comment,
If you want to get student with its corresponding course then
Your get student method look like
public Student GetStudent(int Id)
{
Student student = context.Students.Find(Id);
return new Student
{
StudentID = student.StudentID,
Name = student.Name,
Course = student.Course
};
}
Ad you can access student's course like
Student student = GetStudent(1);
string CourseName = student.Course.Name;
you can use your async and await with above code depending your need.