Global Validation

Input validation in NestJS happens at the DTO layer using class-validator decorators. Apply decorators like @IsNotEmpty, @IsEmail, and @MaxLength to DTO properties, then use NestJS pipes to validate incoming requests automatically before business logic executes, preventing invalid data from reaching your persistence layer.

Implement dedicated validator service classes that check existence and uniqueness constraints against your database. Execute these checks early in your use case logic—before Prisma transactions—to fail fast and avoid unnecessary processing while ensuring data integrity across your application.

Yes. class-validator supports custom decorators for domain-specific rules beyond standard validators. Define custom decorators using @ValidatorConstraint and @Validate to enforce application-specific validation logic declaratively on DTO fields.

Validate all inputs before initiating Prisma transactions. Run DTO validation and business rule checks at the start of your use case, ensuring only vetted data enters transaction scope. This fail-fast approach prevents rollbacks and maintains application stability.

Client validation is easily bypassed. Server-side validation with class-validator and custom rules is essential to prevent security vulnerabilities, data corruption, and application crashes by enforcing data integrity at the API boundary, regardless of client behavior.

class-validator requires class-based DTOs because decorators only function on class instances. Use TypeScript classes with decorators for DTO validation; interfaces are compile-time only and cannot be introspected at runtime where validation occurs.