Can't get dropdown to appear after creating entity

Question

I just wanted to be able for a user to select from a dropdown if their id number was a ssn or ein.

I created a Farm entity and I wanted the user to select from a dropdown using Datalist whether or not it was an EIN or SSN so I created a TPINType (taxpayer id # type) Entity and added it to AppConstants and to the Database and I am not sure if I am missing a data annotation or something but I can't get it to even populate the TPINType on the screen where someone would add their farm

    [UIHint("SelectListModel")]
    [DataMember]
    [Display(AutoGenerateField = false, Name = "TPIN Type")]
    public virtual TPINType TPINType { get; set; }