Apply string extension method on model based on data annotations?

Question

This may well not be possible, but if it is possible it will save me a great deal of time in a large project.

Let's say I have an extension method to format a string. The implementation of the extension method isn't important, but imagine it is this:

public static string AddPrefix(this string input) {
       return string.Format("{0}{1}", "pre_", input);
}

What I would love to be able to do it add a data annotation to a field in my model that I want the extension method to be applied to. I don't want to validate user input to match the format of the extension method, but I want to apply the extension method before submitting the data for any field it would apply to.

For instance, I might have:

public class Person {

    [Prefix]
    public string Forename {get;set;}
}

I would then want to apply the extension method to the forename before submitting the model to a database or webservice.

I'm imagining this isn't possible, so if not can anyone point in the direction of the best way to apply the extension method - there might be up to 50 fields spread across all sorts of classes in my domain model.

when you say 'before submit' are you talking about client side submit to comtroller or submit to data base? — teo van kot, Feb 26 '15 at 20:08
Sorry I should have been clearer - I mean on submit to database (or actually a web service in this instance). — darth_phoenixx, Feb 26 '15 at 20:09
Are you sending (submitting) from controller to web service? — Michael, Feb 26 '15 at 20:15
Generally speaking, yes. There is likely to be mapping from view model to domain model in most instances, but controllers will be handling the submission to the services. — darth_phoenixx, Feb 26 '15 at 20:17

score 1 · Answer 1 · edited May 23 '17 at 11:56

I searched around a little and find this answer that says that you basicaly should not modify value of property from attribute. It just wrong. But here is some way.

public class PrefixAttribute : ValidationAttribute
{
    protected override ValidationResult IsValid(object value, ValidationContext validationContext)
    {
       //try to modify text
            try
            {
                validationContext
                .ObjectType
                .GetProperty(validationContext.MemberName)
                .SetValue(validationContext.ObjectInstance, string.Format("{0}{1}", "pre_", value.ToString()), null);
            }
            catch (System.Exception)
            {                                    
            }

        //return null to make sure this attribute never say iam invalid
        return null;
    }
}

Interesting idea, thanks. I will certainly try this out and see how it goes. — darth_phoenixx, Feb 26 '15 at 20:19

score 1 · Answer 2 · answered Feb 26 '15 at 20:38

1

One option is to leverage Aspect Oriented Programming.

This would not require an extension method.

PostSharp is popular for .NET development.

answered Feb 26 '15 at 20:38

Scott Nimrod

11,206
11
54
118

This definitely looks like it could be a potential solution. Never heard of this before so it looks like I've got some good reading material to keep me going now :) – darth_phoenixx Feb 26 '15 at 20:43
It injects code into your MISL before compiling. Great for logging, security, and any other cross-cutting concerns. – Scott Nimrod Feb 26 '15 at 22:24

score 0 · Answer 3 · answered Feb 26 '15 at 20:27

0

It sounds to me that you want to create a custom data annotation, is that the case?

If so then this presents a possibility.

answered Feb 26 '15 at 20:27

seguya

56
2

A custom data annotation would be perfect, but I don't want it to validate the data. Just a custom data annotation to signify that the value should have the extension method applied to it. – darth_phoenixx Feb 26 '15 at 20:29

Apply string extension method on model based on data annotations?

3 Answers3