Question

I been practicing with EF Code First, SQL Express, and ASP.Net MVC3.

When I run the website first the correct tables are generated by the FooInitializer and Student and Image are populated but for some reason the join table (StudentImages) is not being populated.

What could be the issue?

Tables: Student, Image, and StudentImages

public class Student
{
    public int Id { get; set; }
    public string Name { get; set; }

    public virtual ICollection<Image> Images  { get; set; }
}

public class Image
{
    public int Id { get; set; }
    public string Filename { get; set; }
    public string Extension { get; set; }

    public virtual ICollection<Student> Students { get; set; }
}

public class FooInitializer : DropCreateDatabaseIfModelChanges<DBContext>
{

    protected override void Seed(DBContext context)
    {
    var students = new List<Student> {
        new Student { Id = 1, Name = "John" },
        new Student { Id = 2, Name = "Jane" }
    };

    students.ForEach(s => context.Students.Add(s));
    context.SaveChanges();


    var images = new List<Image> {
    new Image { Id = 1, Filename = "IMG_4596.JPG", Extension = ".jpg" },
        new Image { Id = 2, Filename = "IMG_4600.JPG", Extension = ".jpg" }
    };

    images.ForEach(i => context.Images.Add(i));

    students[0].Images.Add(images[0]);
    context.SaveChanges();
    }
}

Answer 1

From what I can tell your Image class does not have a reference to the StudentID. Try adding:

public int StudentID { get; set; } 

to the Image class maybe?

Also having an ICollection would mean that one image could have multiple students – is this correct? Maybe it should be a public virtual Student Student {…}

EDIT: Also I found this, with a many to many relationship (if thats what you need):

In your OnModelCreating() Method:

modelBuilder.Entity<Student>()
    .HasMany(c => c.Images).WithMany(i => i.Students)
    .Map(t => t.MapLeftKey("StudentId")
        .MapRightKey("ImageID")
        .ToTable("StudentImages"));

taken from this link that states:

A many-to-many relationship between the Instructor and Course
entities. The code specifies the table and column names for the join
table. Code First can configure the many-to-many relationship for you
without this code, but if you don’t call it, you will get default
names such as InstructorInstructorID for the InstructorID column.

EDIT: Here is the code I used the other night, with my implementation of the code first MVC site:

var users = new List<User> 
            {
                new User { UserID = new Guid(), Email = "[e-mail]", LastOnline = DateTime.Now, Password = "pword", RegistrationDate = DateTime.Now, SecurityAnswer = "me", SecurityQuestion = "who?", Roles = new List<Role>() },
            };

            users.ForEach(s => context.Users.Add(s));
            context.SaveChanges();

            var roles = new List<Role>
            {
                new Role { RoleID = "Admin", Description = "Administration Users", Users = new List<User>() }

            };
            roles.ForEach(r => context.Roles.Add(r));


            users[0].Roles.Add(roles[0]);
            context.SaveChanges();



            var userLicense = new List<UserLicense>
            {
                new UserLicense { AddDateTime = DateTime.Now, LicenseType = "Farmer", Manufacturer = "Motorola", Model = "Droid", PhoneIdentifier = "c0e4223a910f", UserID = users[0].UserID, User = new User() }

            };
            userLicense[0].User = users[0];
            userLicense.ForEach(u => context.UserLicenses.Add(u));
            context.SaveChanges();

            userLicense[0].User = users[0];
            context.SaveChanges();

Notice in each instantiated item, I am also instantiating a new referenced item within the parent object.

EDIT:

Ok try this:

var students = new List<Student> {
    new Student { Id = 1, Name = "John", Images = new List<Image>() },
    new Student { Id = 2, Name = "Jane", Images = new List<Image>() }
};

students.ForEach(s => context.Students.Add(s));
context.SaveChanges();


var images = new List<Image> {
    new Image { Id = 1, Filename = "IMG_4596.JPG", Extension = ".jpg", Students = new List<Student>()  },
    new Image { Id = 2, Filename = "IMG_4600.JPG", Extension = ".jpg", Students = new List<Student>() }
};

images.ForEach(i => context.Images.Add(i));

students[0].Images.Add(images[0]);
students[1].Images.Add(images[1]);
context.SaveChanges();