NestJS · Middle · Question 23 of 75

How can a custom validation rule check something asynchronous, like 'email is not taken'?

1With ParseIntPipe
2Validation decorators can't be async
✓Correct answer: With a custom class-validator constraint class (it can be async and use DI with useContainer), though a unique index is still the real guarantee

Explanation

Async checks improve error messages but have race conditions. The database constraint must catch concurrent duplicates.

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