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C# Entity Framework Basics Extending Our Entity Data Model Defining a Many-to-Many Relationship with an Explicit Bridge Entity

Posted by Lee Puckett
Lee Puckett
12,539 Points

Task 3 of 3 Not sure if I am updating the correct properties.

part 1: Update the Courses navigation collection property to be of type CourseStudent.

So my thought was to change public ICollection<Course> Courses {get; set;} to... public CourseStudent Courses {get; set;}

part 2: Update the default constructor to initialize the Courses property to an instance of List<CourseStudent> ....what is the "default constructor"?
I listened for that key word int the video but never hear it.

Course.cs 
using System.Collections.Generic;

namespace Treehouse.CodeChallenges
{
    public class Course
    {
        public Course()
        {
            Students = new List<CourseStudent>();
        }

        public int Id { get; set; }
        public int TeacherId { get; set; }
        public string Title { get; set; }
        public string Description { get; set; }
        public int Length { get; set; }

        public Teacher Teacher { get; set; }
        public ICollection<CourseStudent> Students { get; set; }
    }
}
CourseStudent.cs 
namespace Treehouse.CodeChallenges
{
    public class CourseStudent
    {

        public int Id {get; set;}
        public int CourseId {get;set;}
        public int StudentId {get;set;}
        public Course Course {get;set;}
        public Student Student {get;set;}
        public decimal Grade {get; set;}

    }
}
Student.cs 
using System.Collections.Generic;

namespace Treehouse.CodeChallenges
{
    public class Student
    {
        public Student()
        {
            Courses = new  List<Course>();
        }

        public int Id { get; set; }
        public string FirstName { get; set; }
        public string LastName { get; set; }

        public ICollection<Course> Courses { get; set; }
    }
}

6 Answers

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

You said, "change public ICollection<Course> Courses {get; set;} to... public CourseStudent Courses {get; set;}"

This is like what you already did to the other class in task 2. It's still a collection, but of a different type:

        public ICollection<CourseStudent> Courses { get; set; }

And the "default constructor" is the one which has no parameters. But that's the only constructor either of these classes have, so there's no opportunity for confusion.

Lee Puckett
Lee Puckett
12,539 Points
Lee Puckett
Lee Puckett
12,539 Points

Okay I changed the first part. My confusion was based on:

I thought the type was ICollection<Course> since in every other example, the type precedes the property (e.g. int for ID, string, for FirstName, etc.) therefore I assumed ICollection<Course> was the type. But you are saying in the case of Courses, the type is within the <>? Why is that?

Thanks

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

Before the change, you're right that the type of "Courses" is "ICollection<Course>", which is a collection of "Course" objects. The challenge is asking you to change it to a collection of "CourseStudent" objects. It is still a "ICollection", the brackets enclose what type of thing is in the collection.

This is exactly the same change you already made to the other class in task 2.

Lee Puckett
Lee Puckett
12,539 Points
Lee Puckett
Lee Puckett
12,539 Points

Now if I understand correctly, for the second part of this challenge I need to enter Courses = new List<CoursesStudent>() But where does this go? Does it stand alone or do I paste inside of ()?

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

You're not inserting a new line, just changing the List type in the existing constructor code.

Again, you already did exactly the same exact thing to the other class in task 2.

Lee Puckett
Lee Puckett
12,539 Points

I don't know what the list type is.

Steven Parker
Steven Parker
231,268 Points
Steven Parker
Steven Parker
231,268 Points

The code is provided initially is:

            Courses = new List<Course>();

So the list type is "Course" (inside the <>'s). So you'll be changing that, just like you already did in the other class.

Lee Puckett
Lee Puckett
12,539 Points
Lee Puckett
Lee Puckett
12,539 Points

Do I replace something with it?

Lee Puckett
Lee Puckett
12,539 Points
Lee Puckett
Lee Puckett
12,539 Points

Got it. Thanks!

Lee Puckett
Lee Puckett
12,539 Points
Lee Puckett
Lee Puckett
12,539 Points

I've learned that the body of the constructor is the { } below public Student().

That's good to know because before I thought {Courses = new List<Course>(); } was its own entity and therefore separate from the constructor, causing me to wonder whether I had to add a body ...{ }, that the body was ( ), or that the body was located in open space either above or below the constructor.

Lack of knowledge about the vocabulary and theory force me to use visual patterns for problem solving tools, but like all disciplines, that will only take you so far.