ASP.NET MVC ( Object reference not set to an instance of an object )

Question

I have the following problem when displaying list of personal file, but I used the (using System.Data.Entity) and (Include) in the query it's not working

Class Model

public class PersonalFile
{
    public int Id { get; set; }

    [StringLength(50)]
    public string FileName { get; set; }

    [StringLength(500)]
    public string FilePath { get; set; }

    public DateTime UploadDateTime { get; set; }

    public int EmployeeId { get; set; }

    [ForeignKey("EmployeeId")]
    public Employee Employee { get; set; }

    public int? FileCategoryId { get; set; }
    [ForeignKey("FileCategoryId")]
    public virtual FileCategory FileCategory { get; set; }

}

Class View Model

public class PersonalFileViewModel
{
    public int Id { get; set; }

    [StringLength(50)]
    public string FileName { get; set; }

    [StringLength(500)]
    public string FilePath { get; set; }
    public int EmployeeId { get; set; }

    [Required]
    public int FileCategoryId { get; set; }

    public IEnumerable<PersonalFile> PersonalFiles { get; set; }
}

Class Model File Category

public class FileCategory
{
    public int FileCategoryId { get; set; }

    public string categoryName { get; set; }
    public string optionGroup { get; set; }
    public virtual ICollection<PersonalFile> PersonalFile { get; set; }
}

Action Method public ActionResult Index(int? id) { if (id == null) return HttpNotFound();

        var empl = _dbContext.Employees.SingleOrDefault(c => c.EmployeeId == id);
        if (empl == null)
            return HttpNotFound();

        ViewBag.FileCategoryId = new SelectList(_dbContext.FileCategory, "FileCategoryId", "categoryName" , "optionGroup", 0);

        var vwModel = new PersonalFileViewModel
        {
            EmployeeId = empl.EmployeeId,
            PersonalFiles = _dbContext.PersonalFiles.Include(p => p.Employee).Include(p => p.FileCategory).Where(x => x.EmployeeId == id)
        };


        NameAndImage(empl.EmployeeId);
        return View(vwModel);
    }

View

foreach (var j in Model.PersonalFiles)
                            {
                                <tr style="border-top: 1px solid black;">
                                    <td style="vertical-align: middle;">@j.FileName</td>
                                    <td style="vertical-align: middle;"> @j.FileCategory.categoryName </td>
                                    <td style="vertical-align: middle;">@j.UploadDateTime</td>
                                    <td>
                                        <a [email protected]("~/Content/Images/PersonalFiles/"+j.FilePath) class="btn btn-success btn-sm">Download</a>
                                        @Html.ActionLink("Delete", "Delete", new { j.Id }, new { @class = "btn btn-danger btn-sm", onclick = "return confirm('Do you really want to delete this file?');" })
                                    </td>
                                </tr>

                            }

enter image description here

check if @j.FileCategory is coming null? perhaps thats why it is not retrieving the value of categoryName — Rajan Mishra
Add a temporary line in your controller: _dbContext.PersonalFiles.Include(p => p.Employee).Include(p => p.FileCategory).Where(x => x.EmployeeId == id).ToList(); - is the expected data in here? Is it in the database? — Steve Greene

Nguyễn Văn Phong Nguyễn Văn Phong · Accepted Answer · 2019-12-21T02:04:51

Firstly, make sure that with each PersonalFile belongs to FileCategory accordingly.

Secondly, You should .ToList() to force our query to execute immediately instead.

PersonalFiles = _dbContext.PersonalFiles.Include(p => p.Employee).Include(p => p.FileCategory).Where(x => x.EmployeeId == id).ToList()

ASP.NET MVC ( Object reference not set to an instance of an object )

2 Answers