How do you avoid duplication of validation on the

Question

How do you avoid duplication of validation on the server and client-side? Is there a web programming platform that generates one from the other, so I don't have to keep the two in sync?

Answer 1

What you can do is have the server-side validation logic being run by web services that your client-side validation can call via AJAX and also when you post back to your server.

Answer 2

As others mentioned, you should keep the duplication, as the client-side validation is to help the application react sooner to help the user, but, the real validation is on the server-side, as you should never trust anything passed in until it has been validated. You will probably do more extensive validation on the server-side, esp if there is a need to check against a data source, for example, is the username unique would be on the server-side, but is the username long enough, or an email address, could be done on the client-side, and server-side.

I tend to put in comments when there is duplication, especially if I am using a regular expression, to make certain that what changes in one is changed in another.

Good unit tests will help to ensure that these two will always remain in sync.

Answer 3

There are frameworks that can generate the client-side validation from serverside validation configuration.

Now I don't know what language or frameworks you are using, but maybe this article can be of help: http://www.emadibrahim.com/2008/09/08/client-server-side-validation-in-aspnet-mvc/

He's using Castle Validator Component together with JQuery and adds some glue to generate the clientside validation based on the serverside validation attributes. It's for asp.net mvc.

/Asger

Answer 4

It's best to do validation on the server side in most cases. You have many different options to make this easier such as Ajax or using sticky forms in PHP. I personally tend to do validation on the server side because the user has the option to turn off JavaScript and they can't turn off validation on the server.....

Answer 5

Asp.net Version 1 had validator controls to do what you are asking

http://msdn.microsoft.com/en-us/library/yb52a4x0.aspx

Answer 6

I think the best way is to use a component that offers both. Their code has been tested, and you don't need to maintain it. I have used Peter Blum's controls in the past with great success. Other than that I think you will have to maintain two code bases if you want to offer both. There is a tool called Script# which can help compile C# to Javascript (it does a translation, not a real compilation), but I am not sure how great it would work for this situation.