What is the best way of adding a greater than 0 validator on the client-side using MVC and data annotation?

Question

I'd like to be able to only allow a form to submit if the value in a certain field is greater than 0. I thought maybe the Mvc Range attribute would allow me to enter only 1 value to signify only a greater than test, but no luck there as it insists on Minimum AND Maximum values.

Any ideas how this can be achieved?

Brookbrooke

[Range(int.MinValue, int.MaxValue)] – Lowlife

Answer 1

You can't store a number bigger than what your underlying data type could hold so that fact that the Range attribute requires a max value is a very good thing. Remember that ∞ doesn't exist in the real world, so the following should work:

[Range(1, int.MaxValue, ErrorMessage = "Please enter a value bigger than {1}")]
public int Value { get; set; }

Harridan

The downside of this approach is that if it validates "abcd" it's going to display: Please enter a value less than or equal to 2147483647. – Interpleader

you shouldn't be able to enter letters in a numeric field. The problem i have with this is if i enter 9999999999999999999 it says my number is too small. – Curriculum

Answer 2

I found this answer looking to validate any positive value for a float/double. It turns out these types have a useful constant for 'Epsilon'

Represents the smallest positive System.Double value that is greater than zero.

    [Required]
    [Range(double.Epsilon, double.MaxValue)]
    public double Length { get; set; }

Outmost

Epsilon is actually a calculus function. It is a "limit" function that basically says "the smallest number that can be distinguished from zero" so you could end up with entries of .00000001. I would put a realistic number on the min. – Curriculum

Given that my numbers can be very small, I don't have a way to calculate just how small, and all I want is to ensure I don't get a divide-by-zero error, this Epsilon method is actually exactly what I need – Inebriate

Answer 3

You can create your own validator like this:

    public class RequiredGreaterThanZero : ValidationAttribute
{
    /// <summary>
    /// Designed for dropdowns to ensure that a selection is valid and not the dummy "SELECT" entry
    /// </summary>
    /// <param name="value">The integer value of the selection</param>
    /// <returns>True if value is greater than zero</returns>
    public override bool IsValid(object value)
    {
        // return true if value is a non-null number > 0, otherwise return false
        int i;
        return value != null && int.TryParse(value.ToString(), out i) && i > 0;
    }
}

Then "include" that file in your model and use it as an attribute like this:

    [RequiredGreaterThanZero]
    [DisplayName("Driver")]
    public int DriverID { get; set; }

I commonly use this on dropdown validation. Note that because it's extending validationattribute you can customize the error message with a parameter.

Curriculum

I ended up using this answer for another situation that did require a custom validator. For simple integer greater than zero validation, Darin's answer should be used. – Rizika

I actually prefer his method as well, but the people i work with have an issue with "arbitrarily setting limits" on values. – Curriculum

Ha, that seems strange. I could see their reasoning if the valid range was less than the max integer size. – Rizika

it's more of an issue with decimals. Without looking, i'm pretty sure that one doesn't have a min or max function built in. – Curriculum

This was the best solution for me! – Jacobinism

I've implemented a similar solution but called it simply [Positive], and inherited fromRangeAttribute to utilize framework code as much as possible. – Snip

We actually don't use this ourselves any more. I implemented a generic "required" function that i created an overload for that treats zero as empty if i tell it to. – Curriculum

Answer 4

The above validator works with integers. I extended this to work with a decimal:

    public class RequiredDecimalGreaterThanZero : ValidationAttribute
    {
        /// <summary>
        /// Designed for dropdowns to ensure that a selection is valid and not the dummy "SELECT" entry
        /// </summary>
        /// <param name="value">The integer value of the selection</param>
        /// <returns>True if value is greater than zero</returns>
        public override bool IsValid(object value)
        {
            // return true if value is a non-null number > 0, otherwise return false
            decimal i;
            return value != null && decimal.TryParse(value.ToString(), out i) && i > 0;
        }
    }

Scandalmonger