Data Annotation Phone Number Conversion

Question

I want to gracefully convert phone number input from my users into a specific phone number format.

• I would like convert this with a dataAnnotation, Just as [dataType(dataType.Date)] displays a dateTime as a string

Ie:

• 0205938472 into +61205938472
• 02 0593 8472 into +61205938472
• 0593 8472 into +61205938472 (I will assume the area code from where they live or if its a mobile)
• 02-0593-8472 into +61205938472

Etc, I also want to convert the other direction:

• +61205938472 into 02 0593 8472 (Or whatever format i choose)

I want to do this to promote readability for the user but retain a strict data type in the database.

Questions

1. Is using a dataAnnotation in this manner considered bad practice?
2. How would I actually write the dataAnnotation( /However you would do it)?
   (please include some code)
   Edit: to clarify, i do not want someone to write the extension for me, I would just like an example of key pieces of code and implementation.

Please Note

• These are Australia, New Zealand and internationally formatted numbers being stored as internationally formatted numbers.
• And International Formatted numbers being converted to Australia, New Zealand or internationally formatted depending on the user's location (which i can determine)

Answer 1

You can use DataTypeAttribute like so:

[DataType(DataType.PhoneNumber)]
public string PhoneNumber{get; set;}

Answer 2

Depending on the UI you're using, you might be able to do this using a:

• ASP.NET: Custom binding code (see example)
• ASP.NET MVC: ModelBinder
• WPF: CustomBinder
• Windows Forms: Custom Converters/Editors

As parsing and formatting usually happens in the UI layer, I doubt you will find a solution that works at the data/model layer and which will work universally or which can do more than just validation.

In the data annotations namespace, there is a DataType.PhoneNumber which you can attach to your properties. Though you, yourself, remain responsible to do the parsing and the formatting using the appropriate display technology.

Answer 3

1. Data annotations and datatype are used for validation, not for converting values. The datatype is mostly used so that the validation knows where to start guessing.

2. That is asking too much for someone to code an extension like that, especially without showing any effort.