I am using NestJS, typeORM and MongoDB. I want to write search filters but i see that it is not as proper as I want to.

It is the request DTO SearchLessonDto.ts:

export class SearchLessonDto {
  @Column()
  @Expose({ name: 'title' })
  title: string;

  @Column()
  @Expose({ name: 'categories' })
  @Transform(DecodeStringArray)
  categories: number[];

  @Column()
  @Expose({ name: 'is_published' })
  isPublished: string;

  @Column()
  @Expose({ name: 'type' })
  type: LessonTypeEnum;

  filters(): NonNullable<unknown> {
    const lessonSearchFilter: LessonSearchFilter = new LessonSearchFilter();
    if (this.title) lessonSearchFilter.title = { $regex: this.title };
    if (Array.isArray(this.categories) && this.categories.length)
      lessonSearchFilter.categories = { $in: this.categories };
    if (this.isPublished !== undefined && this.isPublished !== null)
      lessonSearchFilter.isPublished = this.isPublished === 'true';
    if (this.type !== null && this.type !== undefined)
      lessonSearchFilter.type = this.type;

    return lessonSearchFilter;
  }
}

class LessonSearchFilter {
  title: Record<string, string>;
  categories: Record<string, number[]>;
  isPublished: boolean;
  type: LessonTypeEnum;
}

and it is the findAll service function:

  async findAll(
    searchLessonDto: SearchLessonDto,
  ): Promise<LessonResponseDto[]> {
    const lessons: Lesson[] = await this.lessonRepository.find({
      where: searchLessonDto.filters(),
    });

    return lessons.map((lesson: Lesson) => lesson.toResponse());
  }

I just want to you give feedback about what i did here, is it proper way to do it or there other ways?