Reusable nestjs pipe to query data from table

DownloadBlobnameEvidencePipe

import { Injectable, mixin, PipeTransform, Type } from '@nestjs/common'
import { EntityManager, ObjectType } from 'typeorm'
import { BaseEvidence } from '@/entity'
import { EvidenceFile } from '../types'

export function DownloadBlobnameEvidencePipe<T extends BaseEvidence>(type: ObjectType<T>): Type<PipeTransform> {
  @Injectable()
  class EvidenceBlobnamePipe implements PipeTransform<string, Promise<EvidenceFile | undefined>> {
    constructor(private em: EntityManager) {}

    async transform(id: string): Promise<EvidenceFile | undefined> {
      const evidence = await this.em.findOne(type, id)

      if (!evidence) {
        return undefined
      }

      const { downloadBlobname: blobname = '', filename = '' } = evidence || {}
      return {
        blobname,
        filename,
      }
    }
  }
  const Pipe: Type<PipeTransform> = mixin(EvidenceBlobnamePipe)
  return Pipe
}