Cost must be multiple by 5

Question

I am working small application with basic CRUD operation and I have Product Model. In this model I have something like

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

        public string Name { get; set; }

        public int amountAvailable { get; set; }
        public double cost { get; set; }

        [ForeignKey(nameof(User))]
        public int UserId { get; set; }
        public User Users { get; set; }
        
    }

Right now, I need some shortcut or some hack how to make cost (cost of the product), but it should be a multiple of 5, meaning the price can be 5,10,15,20,25,30... etc. Is there anything which I can force user to put price something like thiss? I try with [DataAnnotation] and using Range but I think this will not work.

Answer 1

You can make cost variable as a prop and round there any given value by user till it is valid.

Answer 2

You can use a JS at the end of your view which is probably better as you will have a front end validation rather than posting the form before checking if it’s wrong (sorry I’m using my phone to type the suggested answer so may not be formatted properly) but something like this:

         <script>
                       document.getElementById("Submit_btn_id").addEventListener('click',function ()
                   {

                    //get the value entered in the input field 
                     var userEnterANumber = document.getElementById('input_id').value


                       if (userEnterANumber % 5 == 0)
                      {
                     console.write('This is a multiple of 5')
                         //turn off the required attribute from the input field 
                        document.getElementById("input_id").required = false;
                        }
   
                        else 
                        {
                          console.write('Not a multiple of 5')
                          //set the required attribute on the input field 
                        document.getElementById("input_id").required = true;
                          }
                        });
                </script>