How do you add custom validation?
PICTURE THIS: HOW TO EXPLAIN IT
Simple meaning
I implement ValidationAttribute or IValidatableObject for multi-property rules.
WHY — Validation instead of guessing?
Why interviewers care about Validation:
question about Validation.
trade-offs, and what you would actually do on a .NET MVC project - not buzzwords.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1I implement ValidationAttribute or
IValidatableObject for multi-property rules.
- 2For Core I can
use FluentValidation as a library.
- 3The key is that
ModelState still drives the same if-invalid return View path.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
I implement ValidationAttribute or IValidatableObject for multi-property rules. For Core I can use FluentValidation as a library.