NestJs/Swagger: How to add `additionalProperties: false` on an existing DTO class - nestjs

Question

Hello I am new to Nestjs and trying to implement additionalProperties: false on a DTO class that already has properties on it. I see that the additionalProperties key can be added inside #ApiProperty({ schema: ... { additionalProperties : false} }) but I want to add it like this:
class SomeResponseDto {
#ApiResponseProperty()
text: string;
#ApiResponseProperty()
id: string;
// maybe a new Decorator like this?
#ApiAdditionalProperties(false)
}
...so that only text and id is allowed in the SomeResponseDto. I want to avoid having to define every class as a schema object inside the controllers.
I should note that I'm using express-openapi-validator with nestjs/swagger, and do not want to use the class-validator/class-transformer plugins, so that I can validate responses as well as requests by using just nestjs/swagger decorators.
I have also tried this:
#ApiResponse({
status: 200,
description: 'success',
schema: {
oneOf: [
{
$ref: getSchemaPath(SomeResponseDto),
// additionalProperties: false, <-- this gets ignored
},
],
// additionalProperties: false, <-- this throws OpenApi invalid response errors
},
Is there any easy way to add additionalProperties: false on an existing DTO class?

Answer 1

Here is a workaround: Post this code inside the bootstrap() method of the application
const schemas = document?.components?.schemas;
Object.keys(schemas).forEach((item) => {
if (schemas[item]['properties']?.allowAdditional) {
schemas[item]['additionalProperties'] = true;
} else {
schemas[item]['additionalProperties'] = false;
}
});
This code above will set additionalProperties to false by default.
If for some reason you have a DTO class that you want to allow additionalProperties: true, then inside your DTO Class, add the following decorator and property:
export class SomeResponseDTO {
#ApiPropertyOptional()
allowAdditional?: boolean;
#ApiResponseProperty()
text: string;
#ApiResponseProperty()
id: string;
}
This is a simple solution for true/false case, but can be modified as needed to handle other use cases.
I hope this helps someone!