Where do you do your validation? model, controller or view

Question

Where do you put user input validation in a web form application?

1. View: JavaScript client side
2. Controller: Server side language (C#...)
3. Model

Answer 1

Validation must be done in the controller - it's the only place which assures safety and response.

Validation should be done in the view - it's the point of contact and will provide the best UE and save your server extra work.

Validation will be done on the model - but only for a certain core level of checks. Databases should always reflect appropriate constraints, but it's inefficient to let this stand for real validation, nor is it always possible for a database to determine valid input with simple constraints.