NestJS DTO中公共方法的最佳实践：数据传输与业务逻辑的界限

import { IsString, IsNotEmpty } from 'class-validator';
import { Transform } from 'class-transformer';

export class CreateCustomerDto {
  @IsString()
  @IsNotEmpty()
  @Transform(({ value }) => value.toLowerCase()) // 在数据进入应用前转换为小写
  name: string;

  @IsString()
  @IsNotEmpty()
  email: string;

  // 更多字段...
}

// custom-lowercase.pipe.ts
import { PipeTransform, Injectable, ArgumentMetadata } from '@nestjs/common';

@Injectable()
export class ToLowercasePipe implements PipeTransform {
  transform(value: any, metadata: ArgumentMetadata) {
    if (typeof value === 'string') {
      return value.toLowerCase();
    }
    return value;
  }
}

// create-customer.dto.ts (无需改动)
// create-customer.controller.ts
import { Body, Controller, Post, UsePipes } from '@nestjs/common';
import { CreateCustomerDto } from './create-customer.dto';
import { ToLowercasePipe } from './custom-lowercase.pipe'; // 引入自定义管道

@Controller('customers')
export class CustomersController {
  @Post()
  // 可以在控制器方法或参数级别应用管道
  async createCustomer(@Body(new ToLowercasePipe()) createCustomerDto: CreateCustomerDto) {
    // 此时 createCustomerDto.name 已经是小写
    console.log(createCustomerDto.name);
    // ... 业务逻辑
  }
}

// utils/string.helpers.ts
export function toLowercase(input: string): string {
  return input.toLowerCase();
}

// customer.service.ts
import { Injectable } from '@nestjs/common';
import { CreateCustomerDto } from './create-customer.dto';
// import { toLowercase } from '../utils/string.helpers'; // 如果需要，可以在服务中使用

@Injectable()
export class CustomerService {
  async create(createCustomerDto: CreateCustomerDto) {
    // 假设DTO的name字段已经通过@Transform转换为小写
    const customerName = createCustomerDto.name; 
    const customerEmail = createCustomerDto.email;

    // 如果有其他业务逻辑，可以在这里处理
    // 例如，检查邮箱是否已存在
    // const existingCustomer = await this.customerRepository.findByEmail(customerEmail);
    // if (existingCustomer) { throw new ConflictException('Email already exists'); }

    // 保存客户
    // return this.customerRepository.save({ name: customerName, email: customerEmail });
  }
}