Yii2: Why do validation errors not throw exceptions?

Question

I'm not sure if this is limited to Yii2 or if it could be also discussed with other frameworks or even in general.

In Yii2 I can call validate() on a model object. This will return true or false. If it is false I can call getErrors() to see which validation problems currently exist within this object.

Why is this behavior implemented this way? Why does validate() not throw some ValidationExceptions? I find it also somehow strange that errors are part of the model object. Why are they not part of such an exception?

What are the advantages of this implementation? Why is it done this way? I would prefer exceptions. With this, I could better distinguish between desired and exceptional processing. All that is not desired is handled in catch blocks. The desired happens in try blocks. Isn't this a good idea?

Answer 1

Because in general the errors are used in combination with a form.

Let's say you have a form with some input fields (linked to the model attributes/properties) and you want to do something with these fields, maybe save them or something.

Before saving the fields you would like to verify that they are all valid. When the validate() method is called all attributes are validated one by one and each one will generate an error if needed. If the validation is false and you have an error collection you can again show the form, but this time attach the errors to the fields.

If you throw an exception each time an error occurs your application would stop running and only display the one error. Or you would have to write try-catch blocks for all attributes, which is just unnecessary. When your validation returns true you can run the next step which does the processing and you can be sure all values are valid.

If you really want exceptions you can, of course, write your own Validators (http://www.yiiframework.com/doc-2.0/yii-validators-validator.html)