Button Click System.InvalidCastException

Question

I encountered a

System.InvalidCastException: Unable to cast object of type 'WhereSelectListIterator`2[RateApp.Pages.Index+InQuestion,System.Decimal]' to type 'System.IConvertible'. at System.Convert.ToDecimal(Object value) at RateApp.Pages.Index.Submit()

@page "/"
@using System.Text;
@using System.Net.Http.Headers;
@using Microsoft.AspNetCore.Components;
@using Newtonsoft.Json;
@using RateApp.Models;
@exp
 
<table class="table">
    <thead>
        <tr>
           
            <th>DaysBegin</th>
            <th>DaysEnd</th>
            <th>Interest</th>
            <th>SrInterest</th>
        </tr>
    </thead>
<tbody>
@foreach (InQuestion inques in Questions)
{
    // Pass the Dto properties to the component
     <tr>
                <td>@inques.DaysBegin</td>
                <td>@inques.DaysEnd</td>
                <td>@inques.Interest</td>
                <td>@inques.SrInterest</td>
            </tr>}
</tbody>
</table>
 
 
<div class="row">
    <div class="col-md-3">
        <p>Deposit Amount</p>
    </div>
    <div class="col-md-4">
        <input placeholder="Deposit Amount" @bind="@amount" />
    </div>
</div>
<br />
<div class="row">
    <div class="col-md-3">
        <p>Months</p>
    </div>
    <div class="col-md-4">
        <input placeholder="Months" @bind="@months" />
    </div>
</div>
<div>
    <button type="submit"    @onclick="Submit" >Submit</button>
</div>
<div>
    <div class="col-md-3">
        <p>Interest</p>
    </div>
    <div>@interest</div>
</div>
  
 
@code {
    public class InQuestion
    { 
        public int No { get; set; }
        public int DaysBegin { get; set; }
        public int DaysEnd { get; set; }
        public decimal Interest { get; set; }
        public decimal SrInterest { get; set; }
    }
    public string exp;
    public string codex; public string  jsonstring ; public bool statcode;
    List<InQuestion> Questions = new List<InQuestion>();
    public int number;int months ;decimal interest; int totalquestions;     int     maxnumber;int amount;
    protected override async Task OnInitializedAsync()
    {
        string jwturl = "https://quizapijwt.azurewebsites.net/api/";
        using (var client1 = new HttpClient())
        {
            client1.BaseAddress = new Uri(jwturl);
            client1.DefaultRequestHeaders.Clear();
            client1.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            HttpResponseMessage response = await client1.GetAsync("RateCards");
            if (response.IsSuccessStatusCode)
            {
                //Storing the response details recieved from web api
                jsonstring = await response.Content.ReadAsStringAsync();
                try
                {
                    Questions = JsonConvert.DeserializeObject<List<InQuestion>>(jsonstring);
                }
                catch (Exception ex)
                {   }
                // maxnumber=(from e in Questions select e.No).Max();
            }
        }
    }
    private void Submit()
    {
        try
        { 
        decimal days = months * 30;
        var queryint  = from l in Questions
                       where l.DaysBegin >= days
                          && l.DaysEnd <= days
                       select l.Interest;
        decimal finalint = Convert.ToDecimal(queryint);
        decimal amt = amount;
        decimal factor = 12;
        interest = Decimal.Multiply(amt, finalint) / factor;
        }
        catch (Exception ex)
        {
              exp=ex.ToString();
        }
    }
}
 
 

Answer 1

Your code never executes the LINQ expression. Basically, the code tries convert a query to a decimal. Use the Visual Studio debugger so you can see what happening in the code. This is untested but try...

var queryint  = (from l in Questions
               where l.DaysBegin >= days
                  && l.DaysEnd <= days
               select l.Interest).FirstOrDefault();

In my opinion, you should stop using "var" for a bit and use the actual type. The "var" is hiding what your design is actually producing.

Reference documentation

Query expression basics

Answer 2

@page "/" @using System.Text; @using System.Net.Http.Headers; @using Microsoft.AspNetCore.Components; @using Newtonsoft.Json; @using RateApp.Models; @imint @exp
<table class="table"> <thead> <tr>
        <th>DaysBegin</th>
        <th>DaysEnd</th>
        <th>Interest</th>
        <th>SrInterest</th>
    </tr>
</thead>
<tbody> @foreach (InQuestion inques in Questions) { // Pass the Dto properties to the component <tr> <td>@inques.DaysBegin</td> <td>@inques.DaysEnd</td> <td>@inques.Interest</td> <td>@inques.SrInterest</td> </tr>} </tbody> </table>
<div class="row"> <div class="col-md-3"> <p>Deposit Amount</p> </div> <div class="col-md-4"> <input placeholder="Deposit Amount" @bind="@amount" /> </div> </div> <br /> <div class="row"> <div class="col-md-3"> <p>Months</p> </div> <div class="col-md-4"> <input placeholder="Months" @bind="@months" /> </div> </div> <div> <button type="submit"    @onclick="Submit" >Submit</button> </div> <div> <div class="col-md-3"> <p>Interest</p> </div> <div>@interest</div> </div>
@code { public class InQuestion { public int No { get; set; } public int DaysBegin { get; set; } public int DaysEnd { get; set; } public decimal Interest { get; set; } public decimal SrInterest { get; set; } }
public string exp;
public string codex; public string  jsonstring ; public bool statcode;
List<InQuestion> Questions = new List<InQuestion>();
public int number;int months ;decimal interest; int totalquestions;     int     maxnumber;int amount; decimal imint;
protected override async Task OnInitializedAsync()
{
    string jwturl = "https://quizapijwt.azurewebsites.net/api/";
    using (var client1 = new HttpClient())
    {
        client1.BaseAddress = new Uri(jwturl);
        client1.DefaultRequestHeaders.Clear();
        client1.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
        HttpResponseMessage response = await client1.GetAsync("RateCards");
        if (response.IsSuccessStatusCode)
        {
            //Storing the response details recieved from web api
            jsonstring = await response.Content.ReadAsStringAsync();
            try
            {
                Questions = JsonConvert.DeserializeObject<List<InQuestion>>(jsonstring);
            }
            catch (Exception ex)
            {   }
            // maxnumber=(from e in Questions select e.No).Max();
        }
    }
}
private void Submit()
{
    try
    { 
         
   int  days = (months * 30);
  
var    imint  =  (from l in Questions
                   where l.DaysBegin <= days
                      && l.DaysEnd>= days
                   select l.Interest).FirstOrDefault() ; 
                  
  
    decimal amt = amount;
  
   decimal  finint= Decimal.Multiply(amt, imint) /1200 ;   
    interest=Decimal.Multiply( finint,months);
    
    }
    catch (Exception ex)
    {
          exp=ex.ToString();
    }
}
}

Answer 3

@page "/"
@using System.Text;
@using System.Net.Http.Headers;
@using Microsoft.AspNetCore.Components;
@using Newtonsoft.Json;
@using RateApp.Models;
@exp
 
 
<table class="table">
    <thead>
        <tr>
           
            <th>DaysBegin</th>
            <th>DaysEnd</th>
            <th>Interest</th>
            <th>SrInterest</th>
        </tr>
    </thead>
<tbody>
@foreach (InQuestion inques in Questions)
{
    // Pass the Dto properties to the component
     <tr>
                <td>@inques.DaysBegin</td>
                <td>@inques.DaysEnd</td>
                <td>@inques.Interest</td>
                <td>@inques.SrInterest</td>
            </tr>}
</tbody>
</table>
 
 
<div class="row">
    <div class="col-md-3">
        <p>Deposit Amount</p>
    </div>
    <div class="col-md-4">
        <input placeholder="Deposit Amount" @bind="@amount" />
    </div>
</div>
<br />
<div class="row">
    <div class="col-md-3">
        <p>Months</p>
    </div>
    <div class="col-md-4">
        <input placeholder="Months" @bind="@months" />
    </div>
</div>
<div>
    <button type="submit"    @onclick="Submit" >Submit</button>
</div>
<div>
    <div class="col-md-3">
        <p>Interest</p>
    </div>
    <div>@interest</div>
</div>
  
 
@code {
    public class InQuestion
    { 
        public int No { get; set; }
        public int DaysBegin { get; set; }
        public int DaysEnd { get; set; }
        public decimal Interest { get; set; }
        public decimal SrInterest { get; set; }
    }
 
    public string exp;
    public string codex; public string  jsonstring ; public bool statcode;
    List<InQuestion> Questions = new List<InQuestion>();
    public int number;int months ;decimal interest; int totalquestions;     int     maxnumber;int amount;
    protected override async Task OnInitializedAsync()
    {
        string jwturl = "https://quizapijwt.azurewebsites.net/api/";
        using (var client1 = new HttpClient())
        {
            client1.BaseAddress = new Uri(jwturl);
            client1.DefaultRequestHeaders.Clear();
            client1.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            HttpResponseMessage response = await client1.GetAsync("RateCards");
            if (response.IsSuccessStatusCode)
            {
                //Storing the response details recieved from web api
                jsonstring = await response.Content.ReadAsStringAsync();
                try
                {
                    Questions = JsonConvert.DeserializeObject<List<InQuestion>>(jsonstring);
                }
                catch (Exception ex)
                {   }
                // maxnumber=(from e in Questions select e.No).Max();
            }
        }
    }
    private void Submit()
    {
        try
        { 
        decimal days = months * 30;
        var queryint  = from l in Questions
                       where l.DaysBegin <= days
                          && l.DaysEnd >= days
                       select l.Interest;
        decimal finalint = Convert.ToDecimal(queryint);
        decimal amt = amount;
        decimal factor = 12;
        interest = Decimal.Multiply(amt, finalint) / factor;
        }
        catch (Exception ex)
        {
              exp=ex.ToString();
        }
    }
}
 
 

I changed the code and I am getting System.InvalidCastException