Adding columns to joint tables with payload in MVC - mysql

Question

Evening, I have recently gotten help making my database in MVC on SO (I'm very thankful for that). I have another question, as I'm not in graduate school yet so I don't know the best-practice, I thought someone might in my case.
I am making joint tables between two classes, a User table and a Course table. Put simply, a User can have a Course, and this is being made in my OnModelCreating method of my DbContext class
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new UserMap());
base.OnModelCreating(modelBuilder);
}
<-- snip --> Below is my class for the mappings <-- snip -->
public class UserMap : EntityTypeConfiguration<ApplicationUser>
{
public UserMap()
{
// Primary Key
this.HasKey(m => m.Id);
// UserHasCourse
this.HasMany(m => m.Courses)
.WithMany()
.Map(n =>
{
n.MapLeftKey("UserId");
n.MapRightKey("CourseId");
n.ToTable("UserHasCourse");
});
}
}
What I want to do is be able to add more columns to the UserHasCourse. The question is, how do I do this if the table is being generated here? This will not be the only case where I need to add a column/s that isn't necessarily related to the model (ie. I want to add the columns Credits and Grade, corresponding to the number of credits a user has earned in the course with a grade). I don't want to have Credits and Grade saved in the Courses table (as they only need to be in this joint table).
I can always add in two columns in the Server Explorer, but is there a way I should do this in code (if it is better that way)?

Answer 1

Entity Framework can do LOTS of stuff under the covers. However, this does not necessarily mean it's a good idea to let EF "figure stuff out" for you. I use EF all the time and find the CodeFirst approach a great way to get what you want done. What I would suggest is more of a declarative approach. Tell EF exactly what you want to do.
//Models
public class User
{
public int UserId {get;set;}
public int CourseId {get;set;}
public virtual Course Course {get;set;}
}
public class Course
{
private ICollection<User> _users;
public int CourseId {get;set;}
public string CustomPropOne {get;set;}
public string CustomPropTwo {get;set;}
// mark this as virtual if you want to enable lazy loading
public ICollection<User> Users
{
get{ return _users ?? ( _users = new List<User>()); }
protected set{ _users = value;}
}
}
//Mapping Classes
public class UserMap : EntityTypeConfiguration<User>
{
public UserMap()
{
HasKey(u => u.UserId);
HasRequired(u => u.Course)
.WithMany(c => c.Users)
.HasForeignKey(u => u.CourseId);
}
}
//etc.
By declaring EXACTLY what you want to happen, you ensure your db is setup correctly and it becomes trivial to change/update your db model.
--