C#•3mo ago

✅ NullPointException in the Update/Post method, but not in the Get Method

I started feeling puzzled at this NullPointException in this code

[HttpGet]  
    public IActionResult EditListingJ(int? Id)      
    { 
        try  
        {
            var ListingDTO_DBTable = _context.ListingDTO_DBTable.Find(Id);  
            if (ListingDTO_DBTable != null)  
            {  
                ListingProjectsDTO dtoModelEdit = new ListingProjectsDTO()
                {
                    Id = ListingDTO_DBTable.Id,
                    ListingName = ListingDTO_DBTable.ListingName
                }; 
                Console.WriteLine($"Got it"); //The GET method is fine, it grabs the id 
                return Json(dtoModelEdit);  
            } 
            
            return Json(null);  
            
        }  
        catch (Exception ex)  
        {  
            
            return null;  
        }  
    }  
    
    [HttpPost]  
    public IActionResult EditListingJ(ListingProjectsDTO editedDtoModel)      
    {
        if (ModelState.IsValid)
        {
                 //NullPointException!! why does this line stay always null, I don't understand   
                 ListingProjectsDTO _listingProjectsDtoEdit = _listingProjectsDtoRepository.getListingProjectsDto(editedDtoModel.Id);
                 _listingProjectsDtoEdit.Id = editedDtoModel.Id;
                 _listingProjectsDtoEdit.ListingName = editedDtoModel.ListingName;
                _context.ListingDTO_DBTable.Update(_listingProjectsDto);              
                _context.SaveChanges();  
                return Json(_listingProjectsDto);  
            

        }
        return Json(null);
    }

[HttpGet]  
    public IActionResult EditListingJ(int? Id)      
    { 
        try  
        {
            var ListingDTO_DBTable = _context.ListingDTO_DBTable.Find(Id);  
            if (ListingDTO_DBTable != null)  
            {  
                ListingProjectsDTO dtoModelEdit = new ListingProjectsDTO()
                {
                    Id = ListingDTO_DBTable.Id,
                    ListingName = ListingDTO_DBTable.ListingName
                }; 
                Console.WriteLine($"Got it"); //The GET method is fine, it grabs the id 
                return Json(dtoModelEdit);  
            } 
            
            return Json(null);  
            
        }  
        catch (Exception ex)  
        {  
            
            return null;  
        }  
    }  
    
    [HttpPost]  
    public IActionResult EditListingJ(ListingProjectsDTO editedDtoModel)      
    {
        if (ModelState.IsValid)
        {
                 //NullPointException!! why does this line stay always null, I don't understand   
                 ListingProjectsDTO _listingProjectsDtoEdit = _listingProjectsDtoRepository.getListingProjectsDto(editedDtoModel.Id);
                 _listingProjectsDtoEdit.Id = editedDtoModel.Id;
                 _listingProjectsDtoEdit.ListingName = editedDtoModel.ListingName;
                _context.ListingDTO_DBTable.Update(_listingProjectsDto);              
                _context.SaveChanges();  
                return Json(_listingProjectsDto);  
            

        }
        return Json(null);
    }

` In the Get method it grabs the id but the following Post method it does not and crashes into NullPointException. Seems to me like the GET method was able to refer to the row existing in my DB. However that does not seem to be the case for the Post method. Could anyone help me understand why? My code: https://pastebin.com/pXHYHfKM

Pastebin

using System.Diagnostics;using System.Security.Claims;using Microso...

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

15 Replies

Angius•3mo ago

Your best bet would be using the debugger to see what exactly is null there

Nasdack•3mo ago

    [HttpPost]  
    public IActionResult EditListingJ(ListingProjectsDTO editedDtoModel)

    [HttpPost]  
    public IActionResult EditListingJ(ListingProjectsDTO editedDtoModel)

Show us how you're making this HTTP request from the frontend

Unknown User•3mo ago

Message Not Public

felsokning•3mo ago

In the GET, you're using _context but in your post, you're using _listingProjectsDtoRepository. If you debug it, is _listingProjectsDtoRepository null? I'm not sure why you're using both _context and _listingProjectsDtoRepository. Then you update it using _context? _context.ListingDTO_DBTable.Update(_listingProjectsDto); If I had to guess, without seeing the rest of your code, your DI isn't DI'ing - that's why. Also, why are you injecting an HttpClient, if you're not making any http calls? As everyone else said, above, there's a lot of this code that needs clean-up/fixing.

morry329#OP•3mo ago

*if you debug it, is _listingProjectsDtoRepository null? yes

morry329#OP•3mo ago

see here https://pastebin.com/ztnRjNae

Pastebin

/* JQuery */ function EditListing(Id) { $.get("/Home/Edit...

Pastebin.com is the number one paste tool since 2002. Pastebin is a website where you can store text online for a set period of time.

Unknown User•3mo ago

Message Not Public

morry329#OP•3mo ago

ListingProjectsDTO

public class ListingProjectsDTO 
{
    [System.ComponentModel.DataAnnotations.Key]
    public int? Id { get; set; } // Primary key for DTO

    public string? ListingName { get; set; } // Mapped from ListingName in ListingProjects
 
}

getListingProjectsDto is not a class but a part of interface

public interface IListingProjectsDtoRepository
{
    ListingProjectsDTO getListingProjectsDto(int? Id);
    IEnumerable<ListingProjectsDTO> GetAllEmployee();
    
}

So it explains pretty much why it gives me the nullpointException then

Unknown User•3mo ago

Message Not Public

MODiX•3mo ago

namespace Namespace;

[Attribute]
public class Class
{
    public string PublicField;
    private bool _privateField;    

    public int PublicProperty { get; set; }

    public Class() {} // Constructor

    public void Method(int parameter)
    {
        var localVariable = parameter; 

        int LocalMethod(string param) { return 3; }
    } 
}

namespace Namespace;

[Attribute]
public class Class
{
    public string PublicField;
    private bool _privateField;    

    public int PublicProperty { get; set; }

    public Class() {} // Constructor

    public void Method(int parameter)
    {
        var localVariable = parameter; 

        int LocalMethod(string param) { return 3; }
    } 
}

morry329#OP•3mo ago

DeleteJ is working as I wanted (aka it deletes the entry I don't need anymore), so I might fix it once the edit is fixed Ok I will fix that part later once the Edit is fixed. Some weeks ago, my code needed to check if the HTTP request would hit the controller action while bypassing the frontend. So I forgot to remove that 'remnant' from this experiement One more question, if it should never be a class instance, what should it be instead?

Unknown User•3mo ago

Message Not Public

morry329#OP•3mo ago

ok I see. I would like to work on one thing at the time which is that null

Unknown User•3mo ago

Message Not Public

morry329#OP•3mo ago

alright r/solved r/closed

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✅ NullPointException in the Update/Post method, but not in the Get Method

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