about using "virtual ICollection..." in my model design? - asp.net

Question

I my asp.net mvc HR web apps, in my entity data model, in one page razor view, I have more than one model of data loaded and displayed, for example, in The Employee razor view, I want to display Employee data information on the top, but as the same I also want to display other ralated data with this employee such as Salary, Performance and Reveiw, all of these related data are seperated SQL table which is different EF model.
So to make it simple, one employee profile model has its ralated Salary, Performance and Review model (SQL table), so I use "virtual ICollection" in Employee Profile model.
In Employee Profile model: I have these codes:
public class EmpProfile
{
public int ID { get; set; }
[Display(Name = "Employee Name")]
public string EmpName { get; set; }
[Display(Name = "Employee Number")]
public string EmpNum { get; set; }
[Display(Name = "Employee Title")]
public string EmpTitle { get; set; }
[Display(Name = "Department")]
public virtual ICollection<PerfPlan> PerfPlans { get; set; }
public virtual ICollection<ProgReview> ProgReviews { get; set; }
public virtual ICollection<ProgEvaluation> ProgEvaluations { get; set; }
public virtual ICollection<DevelopPlan> DevelopPlans { get; set; }
}
And in Employee Performance model, I have these codes (Salary and Review model are similar as this one):
public class Performance
{
public int ID { get; set; }
public int EmpProfileID { get; set; }
[Required(ErrorMessage = "{0} is required.")]
[Display(Name = "Name*:")]
public string EmpName { get; set; }
[Required(ErrorMessage = "Please enter your Employee Number.")]
[Display(Name = "Employee No.*:")]
public string EmpNum { get; set; }
......
public virtual EmpProfile EmpProfile { get; set; }
}
Now, after I build them, in my performance contoller, I found this line code in Create method:
ViewBag.EmpProfileID = new SelectList(db.EmpProfiles, "ID", "EmpName");
and in Create view generated by the controller, the EmpProfileID dropdownlist field is generated
#Html.DropDownList("EmpProfileID", String.Empty)
Can anybody tell me why the code ViewBag.EmpProfileID = new SelectList(db.EmpProfiles, "ID", "EmpName"); is generated in Create methed?

Answer 1

Because all the generator knows or cares about is that EmpProfileID is a non-nullable int, so it creates a field to edit it. Since it's the id for a foreign key, it helpfully gives you a list of EmpProfile ids to choose from. If you don't want this field directly editable, you can remove it or change it to a hidden field. You just need to keep in mind that it will need to be set somehow, some way before you check ModelState.IsValid or you'll fail validation.