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C#•12mo ago

CurlyRed(Serzhio)

Hello. I am facing an issue with null exception after calling OnPost method in my razor pages site.

When i call method OnGet i load all of the information about property. public void OnGet(int? id) { Property = pS.GetProperty(id); DownPayment = Property.Price * 0.2m; MaximumLoan = Property.Price - DownPayment; } But when i call method OnPost public IActionResult OnPostCalculateMortgage(int? id) { if (!ModelState.IsValid) { return Page(); } // Determine which strategy to use based on the amount to be borrowed ICalculateStrategy strategy; if (AmountToBorrow > MaximumLoan * 0.5m) { strategy = new FixedRateStrategy(); } else { strategy = new FloatingRateStrategy(); } // Set the strategy and calculate the monthly payments Property.Calculator.SetStrategy(strategy); try { // Calculate the monthly payments List<string> paymentSchedule = Property.Calculator.CalculateMonthlyPayment(AmountToBorrow, LoanTerm); // Add the payment schedule to ViewData to display in the page ViewData["PaymentSchedule"] = paymentSchedule; } catch (InvalidOperationException ex) { // Handle exceptions and add error messages to ModelState ModelState.AddModelError(string.Empty, "An error occurred while calculating the mortgage."); } catch (NegativeLoanTermException ex) { ModelState.AddModelError(string.Empty, "Loan term must be positive and at least 12 months."); } catch (NegativePrincipalException ex) { ModelState.AddModelError(string.Empty, "The amount to borrow must be greater than zero."); } // Return the page with the payment schedule or error messages return Page(); }

31 Replies

CurlyRed(Serzhio)OP•12mo ago

I got the error in the lines where i try to populate object data again on the page <div class="carousel-inner"> @for (var i = 0; i < Model.Property.URL.Count; i++) { <div class="carousel-item @(i == 0 ? "active" : "")"> <img class="d-block w-100" src="@Model.Property.URL[i]" alt="Property image @(i + 1)"> </div> } I tried using sessions and serialising object but it didnt help. Maybe i used it in a wrong way

Angius•12mo ago

Well, do you set the Property, and its URL property when you POST? 'Cause I don't see you doing that (also, use $code to post code)

MODiX•12mo ago

To post C# code type the following: ```cs // code here ``` Get an example by typing $codegif in chat For longer snippets, use: https://paste.mod.gg/

CurlyRed(Serzhio)OP•12mo ago

I am setting Property in my OnGet method, it should stay throught my page, its declared in my page code. But I am not sure about URL.. thanks

Angius•12mo ago

The requests are stateless What it means, is each request you make has a completely clean slate Everything gets reset when you do a POST request Doesn't matter what you set when handling a GET Similarly, everything resets when you do a GET request, everything you set with any other request gets reset

CurlyRed(Serzhio)OP•12mo ago

i tried calling OnGet method in the beginning of the POST request and in the end of it, also i tried using sessions to keep all necessary Data but it still thrown null exception, that my Property is empty

Angius•12mo ago

I don't see you call OnGet anywhere inside of your OnPost

CurlyRed(Serzhio)OP•12mo ago

In the snippet i shared i dont call it, i mean i did it before. Let me do it once again and ill share the code again

 public IActionResult OnPostCalculateMortgage(int? id)
 {
     if (!ModelState.IsValid)
     {
         return Page();
     }

     ICalculateStrategy strategy;
     if (AmountToBorrow > MaximumLoan * 0.5m)
     {
         strategy = new FixedRateStrategy();
     }
     else
     {
         strategy = new FloatingRateStrategy();
     }

     Property.Calculator.SetStrategy(strategy);

     try
     {
         List<string> paymentSchedule = Property.Calculator.CalculateMonthlyPayment(AmountToBorrow, LoanTerm);

         ViewData["PaymentSchedule"] = paymentSchedule;
     }
     catch (InvalidOperationException ex)
     {
         ModelState.AddModelError(string.Empty, "An error occurred while calculating the mortgage.");
     }
     catch (NegativeLoanTermException ex)
     {
         ModelState.AddModelError(string.Empty, "Loan term must be positive and at least 12 months.");
     }
     catch (NegativePrincipalException ex)
     {
         ModelState.AddModelError(string.Empty, "The amount to borrow must be greater than zero.");
     }
     OnGet(id);
     return Page();
 }

 public IActionResult OnPostCalculateMortgage(int? id)
 {
     if (!ModelState.IsValid)
     {
         return Page();
     }

     ICalculateStrategy strategy;
     if (AmountToBorrow > MaximumLoan * 0.5m)
     {
         strategy = new FixedRateStrategy();
     }
     else
     {
         strategy = new FloatingRateStrategy();
     }

     Property.Calculator.SetStrategy(strategy);

     try
     {
         List<string> paymentSchedule = Property.Calculator.CalculateMonthlyPayment(AmountToBorrow, LoanTerm);

         ViewData["PaymentSchedule"] = paymentSchedule;
     }
     catch (InvalidOperationException ex)
     {
         ModelState.AddModelError(string.Empty, "An error occurred while calculating the mortgage.");
     }
     catch (NegativeLoanTermException ex)
     {
         ModelState.AddModelError(string.Empty, "Loan term must be positive and at least 12 months.");
     }
     catch (NegativePrincipalException ex)
     {
         ModelState.AddModelError(string.Empty, "The amount to borrow must be greater than zero.");
     }
     OnGet(id);
     return Page();
 }

Angius•12mo ago

$code

MODiX•12mo ago

To post C# code type the following: ```cs // code here ``` Get an example by typing $codegif in chat For longer snippets, use: https://paste.mod.gg/

CurlyRed(Serzhio)OP•12mo ago

I am calling 'GET' before returning Page() same null ex thrown And actually i got the same error among all of my POST requests in my website and unfortunately i cant solve it with chat gpt or bing

Angius•12mo ago

Well, make sure that pS.GetProperty() doesn't return null And that whatever it does return, has the necessary property

CurlyRed(Serzhio)OP•12mo ago

i have unittest for it and i debugged it in OnGet, it returns correct property object with correct properties belonging to object

Angius•12mo ago

Huh, aight What's pS.GetProperty()?

CurlyRed(Serzhio)OP•12mo ago

It is the method of PropertyService, where I inject PropertyDAL of interface IPropertyDAL

Angius•12mo ago

I mean, sure, but what's the code? I'll be more clear maybe. I'm wondering if it's maybe some async issues, like an async void method somewhere, or an unawaited async call That's the only other situation where I can see a page be rendered before the model's properties are set

CurlyRed(Serzhio)OP•12mo ago

 public Property GetPropertyDetails(int? id)

 public Property GetPropertyDetails(int? id)

It is just method that returns Property type object same for service, just returns result of this method

Angius•12mo ago

What code is inside of this method?

CurlyRed(Serzhio)OP•12mo ago

Just SQL query that retrieves Property object with given id lenght of method exceeds max allowed here

Angius•12mo ago

Oof Any suspicious async code? What I mentioned, async void, unawaited async methods, .Result, etc?

CurlyRed(Serzhio)OP•12mo ago

nothing like that

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();

                string query = "SELECT * FROM Properties WHERE PropertyID = @id";

                using (SqlCommand command = new SqlCommand(query, connection))
                {
                    command.Parameters.Add(new SqlParameter("@id", id));

                    using (SqlDataReader reader = command.ExecuteReader())
                    {

                        while (reader.Read())
                        {
                            List<string> urlList = !string.IsNullOrEmpty(urls) ? urls.Split(';').ToList() : new List<string>();

                            return new Property(pId, name, location, price, type, description, urlList, lat, lng);
                        }
                    }
                }
                return null;
            }

            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                connection.Open();

                string query = "SELECT * FROM Properties WHERE PropertyID = @id";

                using (SqlCommand command = new SqlCommand(query, connection))
                {
                    command.Parameters.Add(new SqlParameter("@id", id));

                    using (SqlDataReader reader = command.ExecuteReader())
                    {

                        while (reader.Read())
                        {
                            List<string> urlList = !string.IsNullOrEmpty(urls) ? urls.Split(';').ToList() : new List<string>();

                            return new Property(pId, name, location, price, type, description, urlList, lat, lng);
                        }
                    }
                }
                return null;
            }

Angius•12mo ago

Huh, okay, let's try something... Make your OnPost... method async Task<IActionResult> and add await Task.Delay(1000); between OnGet(id) and return Page();

CurlyRed(Serzhio)OP•12mo ago

this is the method, i cropped out all of the properties of the objects same error I feel like it dont even get to the OnPost method

Angius•12mo ago

Definitely not async issues, then I'm out of ideas Right, how do you even call this method?

CurlyRed(Serzhio)OP•12mo ago

<form method="post" asp-page-handler="CalculateMortgage">

Angius•12mo ago

Can you just name it OnPost and skip the asp-page-handler? Or do you have another OnPost method already? Also, did you try using the debugger?

CurlyRed(Serzhio)OP•12mo ago

yep, i also have another 2 OnPost methods

Angius•12mo ago

I feel like stepping through the code with a debugger would answer a lot of questions, in hindsight lol

CurlyRed(Serzhio)OP•12mo ago

yes, i put the breakpoint everywhere inside OnPost

Angius•12mo ago

Do they get hit?

CurlyRed(Serzhio)OP•12mo ago

But it didnt hit After i click the button inside Post on page, it throws an error that Property is null, but breakpoint is not hit

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