Many to Many in EF core - ef-core-2.0

Question

I have the following models
public class Student
{
public int Id {get; set; }
public string Name {get; set; }
public ICollection<StudentToCourse> StudentToCourse {get; set; }
}
public class StudentToCourse
{
public int StudentId{get; set; }
public Student Student {get; set; }
public int CourseId{get; set; }
public Course Course {get; set; }
}
public class Course
{
public int Id {get; set; }
public string Name {get; set; }
public ICollection<StudentToCourse> StudentToCourse {get; set; }
}
I want to get a list of all COURSE per student ID, how do I go about doing that?

Answer 1

Short answer: SELECT and match on the Id values. Or programatically -
foreach(Student s in yourstudentList)
{
foreach(StudentToCourse stc in s.StudentToCourse)
{
if(stc.StudentId = s.Id)
//this is one you want, do something with it
}
}
Better answer:
First let's look at your model...
Imagine the underlying database structure.
Your middle table is known as a lookup.
You don't really need the entire Student, nor the entire Course object in it.
Also, your Course object does not need to know about either of the other objects.
If you can imagine three tables in your database you can see how you would logically connect a Student to a Course across the three tables.
Your model is still incomplete though. Within your application you still need a container, in this case a List courseIds. In this way your Student doesn't need to care about all the entries in the Student/Course lookup table, just the ones applicable to the particular Student. And you have an easily accessible object to pull data from, or send updates to, the database.
On initial population of the courseIds collection you would do a
SELECT FROM StudentToCourse where StudentId = x
You can then JOIN on your Course table to pull values such as the Course name.
If you find you need to do a lot of those look ups you may cache your Course list and lower your database traffic at the cost of some ram.
Each time you make a new student you would want to populate their list of course Ids and when committing the student to the database you would save your look up table.
This keeps your objects as lightweight as possible while maintaining their relationships.
There are various ways to write the SELECT statement in your dev environment, search them out and find one you like (or that matches your company's current practices) and get used to consistently using the same one. It will keep your code more readable and manageable.