Nest. JS uses express but not completely

Node.js Provides http The module is used to listen to the port 、 Handle http request , Return response , This is also the main thing it does .

however http Modular api Too primitive , It's cumbersome to process the request response directly based on it , So we will use express Wait for the library to encapsulate a layer .

What this layer does is give request and response Added a lot of methods to handle request responses , Meet the needs of various scenarios , And the routing is processed , and , The call chain of middleware is also provided to facilitate the reuse of some code , The call chain of this middleware is called the onion model .

But this layer does not solve the architecture problem ： What to do when there are more modules , How to manage ？ How to divide Model、View、Controller？ wait .

therefore , use Node.js When doing back-end services, we will pack another layer , Solve architecture problems , The framework of this layer is eggjs（ Ant's ）、midwayjs（ Taobao's ）、nestjs（ foreign ）.

nestjs Is one of the best ：

The bottom of this floor is still express、koa etc. , It's just in those http Based on the framework, the architecture problem is solved additionally .

and nestjs There's another thing I did very well , It doesn't depend on any one http platform , It can switch flexibly .

that nestjs How to switch to the underlying platform ？

Think react How to make vdom Render to canvas、dom、native Of ？

Define a unified interface , Of various platforms render Logic implements these interfaces . This pattern is called adapter pattern .

The adapter pattern is when a function implemented by a third party is used , Don't rely directly on , Instead, define a layer interface , Let the third party adapt to this layer interface . In this way, any scheme adapted to this layer interface can be integrated , It can also provide flexible switching schemes .

Nest.js To the bottom http The platform provides a layer interface （HttpServer）, Defines a bunch of methods used ：

because ts Of interface All methods must be implemented , In order to simplify the , It inherits another layer of abstract classes AbstractHttpAdapter, Define the method to be implemented as abstract Of .

 

then express Or other platforms, such as fastify Just inherit the class of this adapter , To implement the abstract methods , You can access Nest.js in ：

such as ExpressAdapter：

perhaps FastifyAdapter：

These logic are placed in platform-express and platform-fastify In the bag ：

Nest.js The first line of code calls create：

create You will choose one httpAdapter To create a service ：

The default is express：

such , Subsequent calls request and response In the end, all the methods are express Of course. .

For example controller It can be used in @Request Decorator to inject reqeust object , You can call reqeust Various methods of .

import { Controller, Get, Request } from '@nestjs/common';

@Controller('cats')
export class CatsController {
  @Get()
  findAll(@@Request() request: Request): string {
    return 'This action returns all cats';
  }
}

If you want to call some platform specific methods outside the interface ,Nest.js Also support , Then switch to @Req To infuse ：

import { Controller, Get, Req } from '@nestjs/common';

@Controller('cats')
export class CatsController {
  @Get()
  findAll(@@Req() request: Request): string {
    return 'This action returns all cats';
  }
}

What is injected in this way is a specific platform, such as express The native request object , You can use all its methods directly .

Besides , If you really want to use Express Platform specific api Words , stay NestFactory.create You can specify the corresponding type parameters when , In this way, you can do the corresponding type prompt and check ：

But this is coupled to a specific platform , Unless you're sure you won't switch platforms , Otherwise, it's not recommended .

http The platform does this , Empathy ,websocket So is the platform ：

A unified interface is defined , Connect to... Respectively through adapter socketio and websocket, It can switch flexibly ：

Graphic below Nest.js About http 、websocket Platform handling ：

summary

Node.js Provides http The module is used to listen to the port 、 Processing request response , But it's api Too primitive , So we'll wrap it up , stay express This layer provides more easy to use request、response Of api, But this layer doesn't solve the architecture problem , To introduce MVC、IOC And so on , It needs another layer , use Egg.js、Midway.js、Nest.js This higher-level back-end framework , among Nest.js Is the best .

Nest.js At the bottom and http Special design has been made on the integration of the platform , Using adapter mode , Provide a layer interface , Let the underlying platform adapt , In this way, you can flexibly switch between different http The platform .

But it also supports platform specific api, such as controller It can be used in @Req Injected into the underlying request object , When creating a container, you can also pass in the type parameters of the corresponding platform .

Nest.js The default is Express, But it didn't work Express Not exactly , Because you can flexibly switch between other . This is the charm of the adapter pattern .