Where to put validation logic in MVC software architecture

Question

I am actually starting to learn the mvc architecture.

I'm confused on whether to place my username registration validation logic in model or in controller.

I have some sort of status message that would tell the user whether the new username to register is available or not.

My confusion started because most sources say that it should be in the model because it involves the username data to validate before placing it on the database (rather than checking inputs to the username field). However, the status message should respond immediately prior to the change in the username field by user keypress or change, which lead me to think that it should be in the controller because it involves more on user events.

My concern is not actually on the framework to use but on the standard concept involving MVC. Where do I put the username validation logic based on the conditions/premise above?

score 5 · Accepted Answer · answered Nov 11 '11 at 17:56

As Shikhar says, the actual checking of whether the name is acceptable/available is a Model responsibility. The controller can provide an action that is called by some AJAX on the page, so that as each key is pressed, the text on the page is sent to the dedicated controller action which then validates it through the model (anything that touches the database is Model).

There are a couple of things to consider in the view, such as when the user is typing quickly, you should cancel the previous calls before making the new one as this can get confusing.

Also the controller post action that happens when the user submits the form at the end of their data entry should perform the same validation as the AJAX action did just to avoid race conditions between users.

score 4 · Answer 2 · answered Nov 11 '11 at 17:52

4

It should be in the model as you have read yourself. I think you are getting confused between the "validation process" and "validation rules". Validation process will either be in controller on the client side but validation rules are properties of model.

answered Nov 11 '11 at 17:52

shikhar

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In the context of my question. Which part is the validation process and which part is the validation rule? – Neigyl R. Noval Nov 11 '11 at 17:57
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on key press if you check whether the username is valid or not - its validation process. And if you are checking that username is alphanumeric, it a validation rule, which you might have got like this user->validationRule(user) or user->isValid() – shikhar Nov 11 '11 at 18:01
validation has nothing to do with databases. – shikhar Nov 11 '11 at 18:22
I found this question interesting in one point, If I have a situation where the system validates all inputs with a kind of jQuery plugin (Client Side) and then validate again on server side (Model). Validate with jQuery (Client Side) would be validation process and validate in server side (Model would be validation rule). Is that right? – devasia2112 Jan 03 '12 at 21:13
no both are validation process, in one case rules are on the client side (jquery), in the other rules are with the model(server side) – shikhar Jan 04 '12 at 11:54
In other words, the view must be stupid. It can do validation process but has to ask the controller for the validation rules. – David Gras Jul 23 '14 at 23:49

score 0 · Answer 3 · edited May 23 '16 at 10:31

As an addition to @Colin Desmond, a model-instance should never contain 'wrong' data and thus, in my opinion, in an MVC environment should contain validation logic. So that, regardless of the place where an instance of the model is created, it can never be initialized with wrong data and classes that operate on the model instance can rely on its data. The exception is if there is validation logic that is view dependent. View dependent logic (exceptions) should be implemented in the controller.

For example, validation of an email-address should be implemented in the model. However, a model might allow a bank transaction with a negative amount, but view A might not allow a transaction with a negative amount. The logic for this exception should be implemented on the controller.

Where to put validation logic in MVC software architecture

3 Answers3

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