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C# Entity Framework Basics Extending Our Entity Data Model Refining a Model Using Data Annotations

Posted by Larry Singleton
Larry Singleton
18,946 Points

Entity Framework Basics

Link: https://teamtreehouse.com/library/entity-framework-basics/extending-our-entity-data-model/refining-a-model-using-data-annotations

Question:
In Course.cs add data annotation attributes to the Title property in order to make the following model refinements:

    A value will be required and the associated database column will not allow null values
    The string value will not exceed 200 characters in length and the associated database column data type will be nvarchar(200)

Code Given:
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; }
    }
}

Error: 
Bummer! Did you add the 'using' directive for the System.ComponentModel.DataAnnotations namespace?

My Answer:
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; }
        [Required, StringLength(200)]
        public string Description { get; set; }
        public int Length { get; set; }

        public Teacher Teacher { get; set; }
        public ICollection<CourseStudent> Students { get; set; }
    }
}
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; }
    }
}
Larry Singleton
Larry Singleton
18,946 Points

The error appears to be asking me to add a line of code that has nothing to do with what is asked by the question, is this the case or am I missing something?

7 Answers

Larry Singleton
Larry Singleton
18,946 Points

My apologies Im frustrated and taking it out on you

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

Larry Singleton — If you're no longer frustrated, perhaps you would select "best answer" as the one that was most helpful to resolving the issue. :smile:

Larry Singleton
Larry Singleton
18,946 Points
Larry Singleton
Larry Singleton
18,946 Points

If the namespace is needed it should either be already there or a part of the question or asked for in the question. It confuses those of us trying to figure this out. I've had a lot of issues in this course with questions not being specific and found myself over doing answers. It's quite irritating. It will be covered in the course review. I do realize it may be me which would be nothing new.

Thanks for the guidance, I will retry the challenge using your suggestions.

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

To me, having to add the namespace seemed like a realistic real-world scenario one might encounter in development.

Amit Baniya
Amit Baniya
13,505 Points
Amit Baniya
Amit Baniya
13,505 Points

using System.ComponentModel.DataAnnotations; 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; }
    [Required,StringLength(200)]
    public string Title { get; set; }
    [Required,StringLength(200)]
    public string Description { get; set; }
    public int Length { get; set; }

    public Teacher Teacher { get; set; }
    public ICollection<CourseStudent> Students { get; set; }
}

}

Amit Baniya
Amit Baniya
13,505 Points

Get right answer which I have posted above.

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

That namespace is required when using data annotations.

So it's not unrelated, it's an important part of the challenge.

Also, the annotations must come before the item they apply to. You've applied them to the Description here instead of the Title.

Larry Singleton
Larry Singleton
18,946 Points
Larry Singleton
Larry Singleton
18,946 Points

Where is this explained?

A property named Grade of type decimal

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

Out of context that sounds like just a basic object property, like this:

        public decimal Grade { get; set; }
Larry Singleton
Larry Singleton
18,946 Points
Larry Singleton
Larry Singleton
18,946 Points

It should be a part of the question if its required, not assumed the student knows to place it there.

Steven Parker
Steven Parker
231,198 Points
Steven Parker
Steven Parker
231,198 Points

That's a good point, and I've seen that done in other challenges. You might want to make a suggestion to Support about that.

Larry Singleton
Larry Singleton
18,946 Points
Larry Singleton
Larry Singleton
18,946 Points

I'll add it in the course review I'll be filling out after this course is over. Again, thank you for all your assistance you are making this a bit clearer. It's still muddy waters tho =P