class-validator

@seampact/codegen-class-validator writes a decorated DTO class for each schema of your contract, input and output, and NestJS uses the input ones to refuse a bad request before your handler runs.

Used by: NestJS only.

Set up

Install class-validator and class-transformer in your app, and set experimentalDecorators in tsconfig.json as the NestJS page asks. Then point the validators entry at this package.

# seampact.config.yaml, under targets
  - id: validators
    use: "@seampact/codegen-class-validator"
    apis: [notes]

Link it from your server entry, next to types:

    link:
      types: types
      validators: validators

Run npx seampact generate. The classes land in dtos/ under the validators/<api>/ folder of your outDir.

What you get

For the CreateTask schema of the overview, trimmed from dtos/input.ts:

export class CreateTaskDto {
  @IsString()
  @MinLength(1, { message: "Expected at least 1 character." })
  @MaxLength(200, { message: "Expected at most 200 characters." })
  title!: string;

  @contract.ValidateIfPresent()
  @IsInt()
  @contract.SafeInteger()
  @Min(0)
  effort?: number;
}

Each DTO is wrapped in a schemas/ value your server reads, so every validator library looks the same to the server:

export const CreateTaskSchema = adapter.dtoSchema(
  inputDtos.CreateTaskDto,
  "input",
);

The helpers named contract. come from constraints.ts in the same folder. They carry the checks class-validator has no decorator for.

When a check fails

The server converts the plain value to the DTO without coercion and reads each violation. Each one becomes an issue of the 400 body, named by the contract rule the violation carries, never by the decorator.

Native or consistent rules

With the default rules: native, the DTOs use class-validator’s own decorators, which differ from the contract in a few places.

• Lengths skip the variation selectors U+FE0E and U+FE0F: “❤️” counts 1.
• uuid also checks the version and variant digits.
• date-time does not check the calendar, and accepts second 60, a space instead of T and more than 9 fraction digits.
• exclusiveMinimum and exclusiveMaximum have no class-validator rule: they stay the contract’s checks. So do the checks on each item of a list, which report the item’s position.

Set rules: seampact-consistent for the contract’s exact checks (Switch the validator).

Limits

The generator refuses by name a oneOf, a property default, a nullable value other than an opaque one and the other forms in Generate fails. It works on NestJS only.

Next

• Switch the validator.
• The NestJS setup: NestJS.