C# Entity Framework - Code First - Data Object Property Resolves Null

Question

I am developing a multi-tiered, ASP.NET MVC web application, but have not been able to progress further because I am unable to retrieve accurate object representations of my data within my application. Why is this so? I have tried to be as detailed as possible, but please request clarification if you wish to know more. My projects are as follows:

-MyProject.Data
-MyProject.Logic
-MyProject.Objects
-MyProject.Web

---

My entity classes from MyProject.Objects.Entities

public class Report
{
    [Key]
    public int Id { get; set; }
    public string ReportName { get; set; }
    public int ProductId { get; set; }
}

public class Product
{
    [Key]
    public int Id { get; set; }
    public string ProductName { get; set; }
    public ICollection<Report> ProductReports { get; set; }
}

---

My Context from MyProject.Data

public class MyDb : DbContext
{
    public DbSet<Product> Products { get; set; }
    public DbSet<Report> Reports { get; set; }
}

---

My controller from MyProject.Web

 public class HomeController : Controller
{
    MyDb _db = new MyDb();

    public ActionResult Index()
    {
        var model =
            from p in _db.Products
            orderby p.ProductName ascending
            select p;

        return View(model);
    }
}

---

Lastly, my Seed() method from MyProject.Data.Migrations.Configuration

protected override void Seed(MyProject.Data.MyDb context)
    {
        context.Products.AddOrUpdate(r => r.ProductName,
                new Product
                {
                    ProductName = "AAA",
                    ProductReports =
                        new List<Report> { 
                            new Report { ReportName = "Report A" },
                            new Report { ReportName = "Report B" },
                            new Report { ReportName = "Report C" }
                            }
                },
                new Product
                {
                    ProductName = "MSI",
                    ProductReports =
                        new List<Report> { 
                            new Report { ReportName = "Report X" },
                            new Report { ReportName = "Report Z" }
                            }
                });
    }

---

I can not tell why I am unable to get ICollection<Report> ProductReports from MyProject.Objects.Entities.Product to populate with the correct values. Here are my results from Index() in MyProject.Web

---

I thought at first, being slightly new to this framework, that I had some issues relating to the data structure. To my knowledge, my data appears to be set up correctly. Here is my data in SQL server

---

To further demonstrate that the data appears to be correct, I have run the following query to assure myself that the relations are set properly. I will provide the results alongside the query.

SELECT * From Reports INNER JOIN Products ON Reports.ProductId = Products.Id

Answer 1

As mentioned it looks like you are missing the mapping:

public class Product
{
  [Key]
  public int ProductID { get; set; }
  public string ProductName { get; set; }
  public virtual ICollection<Report> ProductReports { get; set; }
}

public class Report
{
  [Key]
  public int ReportID { get; set; }
  public string ReportName { get; set; }
  public int ProductID { get; set; }
  public virtual Product Product { get; set; }
}

The name of the mapping fields must be the same in both tables and the mapping will be done for you automatically using EF. Also you can add a virtual property to the report so that within the report you can call Product.ProductName or whatever.

Hope this helps

Answer 2

It would be something like this:

public class ReportMap : EntityTypeConfiguration<Report>
    {
        public ReportMap()
        {
            // Primary Key
            this.HasKey(t => t.Id);

            // Properties
            this.Property(t => t.ReportName)
                .IsRequired()
                .HasMaxLength(100);

            // Table & Column Mappings
            this.ToTable("Reports");
            this.Property(t => t.Id).HasColumnName("Id");
            this.Property(t => t.ReportName).HasColumnName("ReportName");

            // Relationships
            this.HasRequired(t => t.Product)
                .WithMany(t => t.ProductReports)
                .HasForeignKey(d => d.ProductId);
        }
    }

And change your Report to also have a Product property, like such:

public class Report
{
    [Key]
    public int Id { get; set; }
    public string ReportName { get; set; }
    public int ProductId { get; set; }
    public virtual Product Product { get; set; }
}

Then in your context:

public partial class SomeContext : DbContext
{
    static SomeContext()
    {
        Database.SetInitializer<SomeContext>(null);
    }

    public SomeContext()
        : base("Name=SomeContext")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Configurations.Add(new ReportMap());
    }
}

Answer 3

Here is an example of EF relationship I have working:

public class CourseSection
{
    [Key]
    public int CourseSectionID { get; set; }

    public int CourseID { get; set; }

    public string Title { get; set; }

    public virtual ICollection<SectionContent> SectionContents { get; set; }
}

public class Course
{
    [Key]
    public int CourseID { get; set; }

    [StringLength(50)]
    public string Name { get; set; }

    public virtual ICollection<CourseSection> CourseSections { get; set; }
}