Magical incantation for nestjs swagger plugin generics nestjs

output.json

{
  "openapi": "3.0.0",
  "paths": {
    "/listings": {
      "get": {
        "operationId": "ListingsController_findAll",
        "parameters": [],
        "responses": {
          "200": {
            "description": "",
            "content": {
              "application/json": {
                "schema": {
                  "$ref": "#/components/schemas/FindAllListingsResponse"
                }
              }
            }
          }
        }
      }
    }
  },
...
  "components": {
    "schemas": {
      "FindAllListingsResponse_Listing": {
        "type": "object",
        "properties": {
          "listingId": {
            "format": "int64",
            "type": "integer"
          },
          "address": {
            "type": "string"
          },
          "deviceId": {
            "format": "int64",
            "type": "integer",
            "nullable": true
          }
        },
        "required": [
          "listingId",
          "address",
          "deviceId"
        ]
      },
      "FindAllListingsResponse": {
        "type": "object",
        "properties": {
          "data": {
            "type": "array",
            "items": {
              "$ref": "#/components/schemas/FindAllListingsResponse_Listing"
            }
          }
        },
        "required": [
          "data"
        ]
      }
    }
  }
}

package.json

{
  "name": "api",
  "version": "0.0.1",
  "description": "",
  "author": "",
  "private": true,
  "license": "UNLICENSED",
  "scripts": {
    "build": "nest build",
    "openapi": "nest start -b swc --type-check --config nest-swagger.json",
    "format": "prettier --write \"src/**/*.ts\" \"test/**/*.ts\"",
    "start": "nest start -b swc",
    "start:dev": "nest start --watch -b swc",
    "start:debug": "nest start --debug --watch -b swc",
    "start:prod": "node dist/main",
    "lint": "eslint \"{src,apps,libs,test}/**/*.ts\" --fix",
    "test": "jest",
    "test:watch": "jest --watch",
    "test:cov": "jest --coverage",
    "test:debug": "node --inspect-brk -r tsconfig-paths/register -r ts-node/register node_modules/.bin/jest --runInBand",
    "test:e2e": "jest --config ./test/jest-e2e.json"
  },
  "dependencies": {
    "@nestjs/common": "^10.0.0",
    "@nestjs/config": "^3.2.0",
    "@nestjs/core": "^10.0.0",
    "@nestjs/jwt": "^10.2.0",
    "@nestjs/passport": "^10.0.3",
    "@nestjs/platform-express": "^10.0.0",
    "@prisma/client": "^5.10.2",
    "passport": "^0.7.0",
    "passport-jwt": "^4.0.1",
    "passport-local": "^1.0.0",
    "reflect-metadata": "^0.2.0",
    "rxjs": "^7.8.1"
  },
  "devDependencies": {
    "@nestjs/cli": "^10.0.0",
    "@nestjs/schematics": "^10.0.0",
    "@nestjs/swagger": "^7.3.0",
    "@nestjs/testing": "^10.0.0",
    "@swc/cli": "^0.3.9",
    "@swc/core": "^1.4.2",
    "@types/express": "^4.17.17",
    "@types/jest": "^29.5.2",
    "@types/node": "^20.3.1",
    "@types/passport-jwt": "^4.0.1",
    "@types/passport-local": "^1.0.38",
    "@types/supertest": "^6.0.0",
    "@typescript-eslint/eslint-plugin": "^6.0.0",
    "@typescript-eslint/parser": "^6.0.0",
    "eslint": "^8.42.0",
    "eslint-config-prettier": "^9.0.0",
    "eslint-plugin-prettier": "^5.0.0",
    "jest": "^29.5.0",
    "prettier": "^3.0.0",
    "prisma": "^5.10.2",
    "source-map-support": "^0.5.21",
    "supertest": "^6.3.3",
    "ts-jest": "^29.1.0",
    "ts-loader": "^9.4.3",
    "ts-node": "^10.9.1",
    "tsconfig-paths": "^4.2.0",
    "typescript": "^5.1.3"
  }
}

paginated.dto.ts

// Code derived from https://github.com/nestjs/swagger/issues/86
import {ApiProperty} from "@nestjs/swagger";

// used to infer the Resource type
export type ClassType<T = any> = new (...args: any[]) => T

// apply the appropriate nestjs decorator to signal an array type
export function PaginatedResponse<R, T extends ClassType<R>>(cls: T) {
  class Paginated implements IPaginatedResponse<R> {
    @ApiProperty({
      type: [cls],
    })
    public data: Array<R>;

    public paging: {
      pages: number
      page: number
    }
  }

  return Paginated;
}

your.controller.ts

 @Get()
  async findAll(): Promise<FindAllListingsResponse> {
    const result = await ... // db query exercise for dev 

    const listings = result.map(item => ({
      listingId: item.listingId,
      address: item.address,
      deviceId: item.deviceId,
    }))

    return {
      data: listings,
      paging: {
        page: 1,
        pages: 1,
      },
    }
  }

your.dto.ts

import {PaginatedResponse} from "@src/utils/api.dto";

export class FindAllListingsResponse_Listing {
  listingId: bigint
  address: string
  deviceId: bigint | null
}

// pass the resource you want to return a collection of
// the generics will take care of the rest
export class FindAllListingsResponse extends PaginatedResponse(FindAllListingsResponse_Listing) {}