Difference between symfony2 callbacks and custom validation constraints

Question

As far as I understand a callback is a constraint that you can customise and set to any field for any type of validation.

A custom validation constraint overrides the base constraint class (creating any type of validation on any field)

I'm just not sure what the difference is, why would I use one and not the other? Are there any performance differences too?

Answer 1

I haven't researched the Form Component that much to be aware of any performance differences, but besides that, why you should choose one over the other:

Callbacks

• It is meant to customize the whole validation process, not just the Constraint. For instance, you can set where the error needs to be displayed;
• The target is always a class, you can't use it on a property;
• You can't reuse it, it is only available on that class/entity.

Custom Validator Constraints

• You can reuse it everywhere (as said by @MrGlass, you can even use services as constraint);
• It can be used on a class and property target;
• You can only customize when something fails, not what is done after it fails.