drop down menu - MVC5 DropDownList -

i trying create dropdownlist selection department, based on selected department table should filtered. kind of viewbag example here: http://www.codeproject.com/articles/687061/multiple-models-in-a-view-in-asp-net-mvc-mvc

//controller using system; using system.collections.generic; using system.data; using system.data.entity; using system.linq; using system.net; using system.web; using system.web.mvc; using ucontoso.models;  namespace ucontoso.controllers { public class dashboardcontroller : controller {     private univcontosoentities db = new univcontosoentities();      // get: /student/     public actionresult index()     {         var deptquery = db.faculties.include(f => f.department);         return view(deptquery.tolist());                      }      protected override void dispose(bool disposing)     {         if (disposing)         {             db.dispose();         }         base.dispose(disposing);     } } }  //model(department) namespace ucontoso.models { using system; using system.collections.generic; using system.componentmodel;  public partial class department {     public department()     {         this.courses = new hashset<course>();         this.faculties = new hashset<faculty>();     }      public int departmentid { get; set; }     [displayname("department")]     public string departmentname { get; set; }       public virtual faculty faculty { get; set; }     public virtual icollection<course> courses { get; set; }     public virtual icollection<faculty> faculties { get; set; } } }  //model (faculty) namespace ucontoso.models { using system; using system.collections.generic; using system.componentmodel;  public partial class faculty {      public faculty()     {         this.courses = new hashset<course>();         this.courses1 = new hashset<course>();     }      public int facultyid { get; set; }     [displayname("faculty lastname")]     public string lastname { get; set; }     [displayname("faculty firstname")]     public string firstname { get; set; }     public system.datetime hiredate { get; set; }       public virtual department department { get; set; }     public virtual icollection<course> courses { get; set; }     public virtual icollection<course> courses1 { get; set; }      public int departmentid { get; set; } } }   //view @model ienumerable<ucontoso.models.faculty>  @{ viewbag.title = "index"; }  <h2>index</h2>  //dropdownlist doesn't work: should select department , filter table <p> @html.dropdownlist("department", "select") </p>   <table class="table"> <tr>     <th>         @html.displaynamefor(model => model.department.departmentname)     </th>     <th>         @html.displaynamefor(model => model.lastname)     </th>     <th>         @html.displaynamefor(model => model.firstname)     </th>  </tr>  @foreach (var item in model) {     <tr>         <td>             @html.displayfor(modelitem => item.department.departmentname)         </td>         <td>             @html.displayfor(modelitem => item.lastname)         </td>         <td>             @html.displayfor(modelitem => item.firstname)         </td>     </tr> }  </table>