Exceptions for validation?

knowj

I have been Googleing around on this debate and most of the results are .NET framework based but the same logic applies. Is validation a case (excuse the pun) for exceptions or basic logic based error reporting?

I have always handled validation within an object method and process the errors in 1 of 2 ways.
1: build the errors into $this->error and if it's populated $this->validate() return 0 and a method is called to return the errors to the user.
2: If an error is found return 0 and report the error to the user via the $this->error object variable/method

They are both similar. The debate seems to be 50/50 from what I can see on using exceptions for validation but do the same rules apply to PHP?

Is user data validation to common an error for the expense of an exception?

laserlight

When we are talking about form validation, I consider invalid input as something "expected", thus exceptions are not appropriate. On the other hand, you would also perform validation of input that would normally have expected values, but can be tampered by the user (e.g., page numbers, or maybe hidden form fields that users should not normally be tampering with), in which case throwing an exception may be appropriate (but for page numbers, it is usually easier to silently set an invalid page number to the first or last page instead of complaining to the user).

knowj

A blog I read that seemed to conclude quite well was something along the lines of.

I expect users to enter stupid data into my forms so it's not an exception if something happens more than 1/1000 times/uses it's expected not an exception.

However the community seems to be tied but I agree with you completely sometimes handling the validation error gracefully by giving the users a first or last page in your example is better than halting everything and throwing/catching an exception.

Until recently I have always handled errors without exceptions (error logs, functions etc...) and currently feeling my way into their uses/best practice.

Forms/user input data are still to this day every coders/programmers nightmare you have to plan for everything and then plan some more as there is always that 1 person that will find how to break it.

NogDog

FWIW, I'm in the camp that exceptions are for programmer mistakes, errors are for user mistakes. 🙂

laserlight

NogDog wrote:
I'm in the camp that exceptions are for programmer mistakes, errors are for user mistakes.

Some programmer mistakes, e.g., argument pre-condition violation for a function that is implementation detail, should be checked with assertions instead, but to be honest I often forget to use them.