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 model to the database (EF6) and create some logic while saving, but I think it is better to validate if the correct value is set before I make a call to the database. Does data annotations provide an attribute like Range but then for specific string values like in the example below? Or do I have to write my own validator attribute?

public class Person {
    public int PersonID { get; set; }

    [Required]
    public string FirstName { get; set; }
    public string LastName { get; set; }

    [StringRange("M","F")]
    public string Gender { get; set; }
}

In the above example, when a post is done to the controller, the only values to accept are "M" or "F".

You can use RegExes see stackoverflow.com/questions/8244572/… — MajkeloDev
– MajkeloDev, Commented Oct 7, 2015 at 8:19
you can also create custom validation attribute youtube.com/watch?v=vcX8WW4fL1s — vijay shiyani
– vijay shiyani, Commented Oct 7, 2015 at 8:27

Simon Wosko · Accepted Answer · 2018-04-27 02:05:53Z

48

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);
    }
}

answered Apr 27, 2018 at 2:05

Simon Wosko

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2 Comments

ClaytonQ Over a year ago

For AllowableValues?.Contains() I had better luck with AllowableValues?.Any(). I love this solution, Simon!

Jan Over a year ago

ErrorMessage defined in the attribute is ignored and instead the content of msg variable is displayed when you do not enter any of the allowable values.

kwv84 · Accepted Answer · 2015-10-07 14:56:28Z

16

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");
        }
    }
}

answered Oct 7, 2015 at 14:56

kwv84

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Comments

tletle · Accepted Answer · 2020-03-06 08:30:53Z

12

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; }

answered Mar 6, 2020 at 8:30

tletle

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2 Comments

Ed Graham Over a year ago

Nice. Quick 'n' dirty, and ideal for my present project!

Sheriff Over a year ago

What else if you have passed m|f. It will get failed. What need to add in lower case two get it pass ?

Bahaa Samoudi · Accepted Answer · 2021-03-17 09:33:40Z

5

[Required]
[RegularExpression("value1|value2|value3|...", ErrorMessage = "YourMessageHere")]
public string Gender { get; set; }

answered Mar 17, 2021 at 9:33

Bahaa Samoudi

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