Data annotation to replace property's value?

Question

Is it possible to use Data Annotation attribute to manipulate text and return a new one after manipulation?

For example I want to validate a string property for having special characters or multiple spaces between words then return a new string to replace the original property's value.

How possible is that using Data Annotation?

Can't you just do it inside the get/set part? `Property { get { return _Property.Replace(badChar, goodChar); } }` — Corak, Mar 21 '13 at 07:05
I think a better approach is a DataBinder: http://stackoverflow.com/a/1734025/7720 — Romias, Apr 13 '17 at 20:17

score 4 · Answer 1 · answered Feb 16 '16 at 20:00

A bit late to answer (2 years!), but yes you can modify the value being validated in a custom DataAnnotations attribute. The key is overriding the IsValid(Object, ValidationContext) method of ValidationAttribute and performing a little reflection magic:

public class MyCustomValidationAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext ctx)
    {
        // get the property
        var prop = ctx.ObjectType.GetProperty(ctx.MemberName);

        // get the current value (assuming it's a string property)
        var oldVal = prop.GetValue(ctx.ObjectInstance) as string;

        // create a new value, perhaps by manipulating the current one
        var newVal = "???";

        // set the new value
        prop.SetValue(ctx.ObjectInstance, newVal);

        return base.IsValid(value, ctx);
    }
}

`ValidationContext` is `null` for me? :/ – Syed Ali Taqi Jun 27 '19 at 10:00 — Syed Ali Taqi, Jun 27 '19 at 10:00

score 1 · Answer 2 · answered Mar 21 '13 at 07:48

1

Corak's suggestion is the best way to do it. However, you can write your base class and using reflection you can do whatever you want with the contents of type members.

answered Mar 21 '13 at 07:48

score 0 · Answer 3 · edited May 23 '17 at 11:54

0

This isn't with a data annotation but just an attribute.

So yes via various methods already discussed here:

How to get and modify a property value through a custom Attribute? Change Attribute's parameter at runtime

It's interesting to note the various solutions from validation to sub classes to 'you can't'

edited May 23 '17 at 11:54

Community

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answered Mar 21 '13 at 07:44

Adam Tuliper

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roydukkey · Answer 4 · 2017-04-13T20:10:33.170

Here is a package that will probably have what you are expecting: Dado.ComponentModel.Mutations

This example will ensure invalid characters are removed from a string. It doesn't introduce validation, but the System.ComponentModel.Annotations can be used alongside Dado.ComponentModel.Mutations.

public partial class ApplicationUser
{
    [ToLower, RegexReplace(@"[^a-z0-9_]")]
    public virtual string UserName { get; set; }
}

// Then to preform mutation
var user = new ApplicationUser() {
    UserName = "M@X_speed.01!"
}

new MutationContext<ApplicationUser>(user).Mutate();

After the call to Mutate(), user.UserName will be mutated to mx_speed01.

Data annotation to replace property's value?

4 Answers4