Using DataAnnotations to compare two model properties

Question

How would I go about writing a custom ValidationAttribute that compares two fields? This is the common "enter password", "confirm password" scenario. I need to be sure the two fields are equal and to keep things consistent, I want to implement the validation via DataAnnotations.

So in pseudo-code, I'm looking for a way to implement something like the following:

public class SignUpModel
{
    [Required]
    [Display(Name = "Password")]
    public string Password { get; set; }

    [Required]
    [Display(Name = "Re-type Password")]
    [Compare(CompareField = Password, ErrorMessage = "Passwords do not match")]
    public string PasswordConfirm { get; set; }
}

public class CompareAttribute : ValidationAttribute
{
    public CompareAttribute(object propertyToCompare)
    {
        // ??
    }

    public override bool IsValid(object value)
    {
        // ??
    }
}

So the question is, how do I code the [Compare] ValidationAttribute?

Answer 1

There is a CompareAttribute in the ASP.NET MVC 3 Framework that does this. If you are using ASP.NET MVC 2 and targeting .Net 4.0 then you could look at the implementation in the ASP.NET MVC 3 source code.

Answer 2

Make sure that your project references system.web.mvc v3.xxxxx.

Then your code should be something like this:

using System.Web.Mvc;

. . . .

[Required(ErrorMessage = "This field is required.")]    
public string NewPassword { get; set; }

[Required(ErrorMessage = "This field is required.")]
[Compare(nameof(NewPassword), ErrorMessage = "Passwords don't match.")]
public string RepeatPassword { get; set; }

Answer 3

This is a longer version of Darin's answer:

public class CustomAttribute : ValidationAttribute
{    
    public override bool IsValid(object value)
    {
        if (value.GetType() == typeof(Foo))
        {
           Foo bar = (Foo)value;
           //compare the properties and return the result
        }

        throw new InvalidOperationException("This attribute is only valid for Foo objects");
    }
}

and usage:

[MetadataType(typeof(FooMD))]
public partial class Foo
{
     ... functions ...
}

[Custom]
public class FooMD
{
     ... other data annotations ...
}

The error will display in @Html.ValidationSummary(false)

Answer 4

You could have a custom validation attribute and apply it on the model and not on individual properties. Here's an example you might take a look at.

Answer 5

if you guys are using MVC 4 please try this code .. it will solve your error..

please make one Metadataclass than in partial class impliment comfirmemail properties . check the below code for more details.

using System;
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;
    using StringlenghtMVC.Comman;
    using System.Web.Mvc;

using System.Collections;

    [MetadataType(typeof(EmployeeMetaData))] //here we call metadeta class
    public partial class Employee
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public string Email { get; set; }
        public Nullable<int> Age { get; set; }
        public string Gender { get; set; }
        public Nullable<System.DateTime> HireDate { get; set; }

       //[CompareAttribute("Email")]
        public string ConfirmEmail { get; set; }
    }

    public class EmployeeMetaData
    {
        [StringLength(10, MinimumLength = 5)]
        [Required]
        //[RegularExpression(@"(([A-za-Z]+[\s]{1}[A-za-z]+))$", ErrorMessage = "Please enter Valid Name")]
        public string Name { get; set; }

        [Range(1, 100)]
        public int Age { get; set; }
        [CurrentDate]
        [DisplayFormat(DataFormatString = "{0:d}", ApplyFormatInEditMode = true)]
        public DateTime HireDate { get; set; }

        //[RegularExpression(@"^[\w-\._\%]+@(?:[\w]{2,6}$")]
        public string Email { get; set; }

        [System.Web.Mvc.CompareAttribute("Email")]
        public string ConfirmEmail { get; set; }


    }

Answer 6

For future people looking at this issue, I was trying to write a validation attribute that would evaluate a regex if an object's property were a certain value. In my case, if an address was a shipping address, I didn't want PO Boxes enabled, so this is what I came up with:

Usage

[Required]
public EAddressType addressType { get; set; } //Evaluate Validation attribute against this

[EvaluateRegexIfPropEqualsValue(Constants.NOT_PO_BOX_REGEX, "addressType", EAddressType.Shipping, ErrorMessage = "Unable to ship to PO Boxes or APO addresses")]
public String addressLine1 { get; set; }

And here's the code for the validation attribute:

[AttributeUsage(AttributeTargets.Property | AttributeTargets.Field, AllowMultiple = false)]
public class EvaluateRegexIfPropEqualsValue : ValidationAttribute
{
    Regex _regex;
    string _prop;
    object _targetValue;

    public EvaluateRegexIfPropEqualsValue(string regex, string prop, object value)
    {
        this._regex = new Regex(regex);
        this._prop = prop;
        this._targetValue = value;
    }

    bool PropertyContainsValue(Object obj)
    {
        var propertyInfo = obj.GetType().GetProperty(this._prop);
        return (propertyInfo != null && this._targetValue.Equals(propertyInfo.GetValue(obj, null)));
    }

    protected override ValidationResult IsValid(object value, ValidationContext obj)
    {
        if (this.PropertyContainsValue(obj.ObjectInstance) && value != null && !this._regex.IsMatch(value.ToString()))
        {
            return new ValidationResult(this.ErrorMessage);
        }
        return ValidationResult.Success;
    }
}