Custom Class Serializer Interceptor (support for automatically adding user roles)

custom-class-serializer.interceptor.ts

import {
  Injectable,
  ExecutionContext,
  CallHandler,
  ClassSerializerInterceptor,
  PlainLiteralObject,
} from '@nestjs/common';
import { Request } from 'express';
import { Observable } from 'rxjs';
import { map } from 'rxjs/operators';

@Injectable()
export class CustomClassSerializerInterceptor extends ClassSerializerInterceptor {
  intercept(context: ExecutionContext, next: CallHandler): Observable<unknown> {
    const request = context.switchToHttp().getRequest<Request>();

    const user = request.user;

    const groups = user ? [user.role.toString()] : [];

    const contextOptions = this.getContextOptions(context);

    const options = {
      ...this.defaultOptions,
      ...contextOptions,
      groups: [...groups, ...(contextOptions?.groups ?? [])],
    };

    return next
      .handle()
      .pipe(
        map((res: PlainLiteralObject | PlainLiteralObject[]) =>
          this.serialize(res, options),
        ),
      );
  }
}