Validate model on specific string values

Question

I\'m working on a Web API 2 project. besides the requirement that some properties are required, some only can have specific values. One option is that I could try to save the m

Answer 1

To validate the Gender property I've created a custom validation attribute by creating a new class (attribute):

using System;
using System.Collections.Generic;
using System.Web;
using System.ComponentModel.DataAnnotations;    

namespace MyProject.Models.Validation
{

    public class StringRangeAttribute : ValidationAttribute
    {
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {

            if(value.ToString() == "M" || value.ToString() == "F")
            {
                return ValidationResult.Success;
            }


            return new ValidationResult("Please enter a correct value");
        }
    }
}

Answer 2

you can use reqular expression like this:

[RegularExpression("M|F", ErrorMessage = "The Gender must be either 'M' or 'F' only.")]
public string Gender { get; set; }

but in my api it will show error message when i passed data so you can add

[StringLength(1, MinimumLength = 1, ErrorMessage = "The Gender must be 1 characters.")]

final code:

[StringLength(1, MinimumLength = 1, ErrorMessage = "The Gender must be 1 characters.")]
[RegularExpression("M|F", ErrorMessage = "The Gender must be either 'M' or 'F' only.")]
public string Gender { get; set; }

Answer 3

In case anyone stumbles upon this thread in the future, I took it a little further and added a public string array property accepting the allowable values in the validation filter. This will allow you to provide a collection of valid strings in the attribute decorator.

This way, you now have a generic reusable attribute you can use anytime to limit a model string property to a predefined set of values. Since it's a validation attribute, you can decorate it with a more informative error message as well.

Example Usage:

public class Person {
    [StringRange(AllowableValues = new[] { "M", "F" }, ErrorMessage = "Gender must be either 'M' or 'F'.")]
    public string Gender { get;set; }
}

String Attribute:

public class StringRangeAttribute : ValidationAttribute
{
    public string[] AllowableValues { get; set; }

    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
        if (AllowableValues?.Contains(value?.ToString()) == true)
        {
            return ValidationResult.Success;
        }

        var msg = $"Please enter one of the allowable values: {string.Join(", ", (AllowableValues ?? new string[] { "No allowable values found" }))}.";
        return new ValidationResult(msg);
    }
}