using a ViewModel giving null exception error

Question

I am using this view model:

public class CaseComplaintsViewModel
{
    public int CasesID { get; set; }
    public int CaseComplaintID { get; set; }
    public string ComplaintCode { get; set; }
    public string ComplaintType { get; set; }
}

This is the view that uses the view model.

@model IEnumerable<cummins_db.ViewModels.CaseComplaintsViewModel>

<table width="100%">
    <tr>
        <th></th>
        <th></th>
        <th>Complaint Code</th>
        <th>Complaint Description</th>
        <th>Delete</th>
    </tr>  
    @foreach (var item in Model)
    {
        <tr>
            <td>
                @Html.HiddenFor(modelItem => item.CasesID )    
            </td>
            <td>
                @Html.HiddenFor(modelItem => item.CaseComplaintID )    
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.ComplaintCode )    
            </td>
            <td>
                @Html.DisplayFor(modelItem => item.ComplaintType)
            </td>
            <td>
                @Ajax.ActionLink("Delete", "RemoveCodeFromCase", "Cases", new {    caseid           item.CasesID, id = item.CaseComplaintID }, null)
            </td>        
        </tr>
    }
</table>

This is my controller action that returns this partial view to the main view:

public ActionResult SelectForCase(int caseid, int compid)
{
    if (ModelState.IsValid)
    {
        CaseComplaint c = new CaseComplaint
        {
            CasesID = caseid,
            ComplaintCodeID = compid
        };
        db.CaseComplaints.Add(c);
        db.SaveChanges();

        var data = (from C in db.CaseComplaints
                    where C.CasesID == caseid
                    select C).ToList().Select( x => new CaseComplaintsViewModel()
                    {
                        CasesID = x.CasesID,
                        CaseComplaintID = x.ComplaintCodeID,
                        ComplaintCode = x.ComplaintCode.ComplaintCodeName,
                        ComplaintType = x.ComplaintCode.ComplaintType
                    }).ToList();

        return PartialView("_CaseComplaintCodes", data);
    }

    return PartialView("_CaseComplaintCodes");
}

After the db.SaveChanges when I try to load the ViewModel I get a null exception on the line ComplaintCode = x.ComplaintCode.ComplaintCodeName

This view model is intended to return a view of CaseComplaints and the ComplaintCode models.

Breakpoints in the code show the ComplaintCode is not loaded. I know I am missing something but not sure what.

Thanks

******EDIT******** This is my case model

public class Cases
    {
    //case data model for call center
    //implement lists for all related child tables too

    [Key]
    public int CasesID { get; set; }

    public string CaseNumber { get; set; }

    [Required(ErrorMessage = "Customer is Required")]
    public int CustomerID { get; set; }
    public virtual Customer Customer { get; set; }

    [MaxLength(50)]
    public string UserName { get; set; }  //get user name from the aspnet membership

    [Required(ErrorMessage = "Case Category is Required")]
    public int CaseCategoryID { get; set; }

    public int TechnicianID { get; set; }
    public virtual Technician Technicians { get; set; }

    [Required(ErrorMessage = "Engine Model is Required")]
    public int EngineModelID { get; set; }
    public virtual EngineModel EngineModel { get; set; }

    [MaxLength(50)]
    public string BMSWorkorder { get; set; }

    [MaxLength(50)]
    [Required(ErrorMessage = "Status is Required")]
    public string CaseStatus { get; set; }

    [MaxLength(50)]
    public string OpenedBy { get; set; }

    [Required(ErrorMessage = "Opened Date is Required")]
    [DataType(DataType.DateTime)]
    public DateTime? OpenedDate { get; set; }

    [MaxLength(50)]
    public string ClosedBy { get; set; }

    [DataType(DataType.DateTime)]
    public DateTime? ClosedDate { get; set; }

    [MaxLength(50)]
    [Required(ErrorMessage="Caller First Name is Required")]
    public string CallerFirstName { get; set; }

    [MaxLength(50)]
    [Required(ErrorMessage = "Caller Last Name is Required")]
    public string CallerLastName { get; set; }

    [MaxLength(100)]
    public string AdditionalContact { get; set; }

    [MaxLength(10)]
    [Required(ErrorMessage = "Qualified is Required")]
    public string Qualified { get; set; }

    public string Description { get; set; }

    [MaxLength(50)]
    [Required(ErrorMessage = "ESN is Required")]
    public string ESN { get; set; }

    [MaxLength(50)]
    [Required(ErrorMessage = "Mileage is Required")]
    public string Mileage { get; set; }

    [DataType(DataType.Date)]
    public DateTime? DateInService { get; set; }

    [MaxLength(50)]
    public string ESTR { get; set; }

    [MaxLength(50)]
    public string EDS { get; set; }

    [MaxLength(50)]
    public string GensetSerialNumber { get; set; }

    [MaxLength(50)]
    public string GensetModelNumber { get; set; }

    //child Case Notes records
    public virtual ICollection<CaseNotes> CaseNotes { get; set; }

    //child case attachment records
    public virtual ICollection<Attachment> Attachments { get; set; }

    //child case complaint records
    public virtual ICollection<CaseComplaint> CaseComplaint { get; set; }

    //tracking fields
    public DateTime? CreatedOn { get; set; }
    [MaxLength(50)]
    public string CreatedBy { get; set; }
    public DateTime? ModifiedOn { get; set; }
    [MaxLength(50)]
    public string ModifiedBy { get; set; }
    }

This is my case complaint model

public class CaseComplaint
    {
    [Key]
    public int CaseComplaintID { get; set; }
    public int CasesID { get; set; }
    public int ComplaintCodeID { get; set; }
    public virtual Cases Cases { get; set; }
    public virtual ComplaintCode ComplaintCode { get; set; }
    }

this is my complaintcode model

public class ComplaintCode
        {
        public int ComplaintCodeID { get; set; }

        [MaxLength(50)]
        [Required(ErrorMessage="Complaint Code is required")]
        public string ComplaintCodeName { get; set; }

        [MaxLength(50)]
        [Required(ErrorMessage="Complaint Type is required")]
        public string ComplaintType { get; set; }

        public virtual ICollection<CaseComplaint> CaseComplaint { get; set; }

        }

Answer 1

the inserted entity is used in your later select, and its navigation properties can't be loaded. That only works on entities loaded from database. You if you disposed the object context and created a new one it would work. Or you could try this select instead:

var data = (from C in db.CaseComplaints
            where C.CasesID == caseid
            select new CaseComplaintsViewModel()
                    {
                        CasesID = C.CasesID,
                        CaseComplaintID = C.ComplaintCodeID,
                        ComplaintCode = C.ComplaintCode.ComplaintCodeName,
                        ComplaintType = C.ComplaintCode.ComplaintType
                    }).ToList();

There are also some options to refresh entities from the database, not sure that would work, but it's one more db query you don't need. This doesn't do anything.

Answer 2

It is a problem with the data coming from your data context. using Visual studio breakpoints, check db.CaseComplaints.ToList() and see each item has a valid ComplaintCode property which is not null.