如何在TypeScript中键入node-postgres异步查询函数? [英] How to type node-postgres async query functions in TypeScript?

问题描述

我对TypeScript相当陌生，并开始将现有服务器从ES6转换为TypeScript.我有点迷茫，试图弄清楚如何为异步函数声明类型.这是ES6代码的存根:

I am fairly new to TypeScript and started to convert my existing server from ES6 to TypeScript. I am a bit lost and trying to figure out how to declare types for async functions. Here's a stub from the ES6 code:

// db.js
import { Pool } from 'pg';

const pool = new Pool({
  connectionString: 'process.env.DB_CONNECTION',
});

export default {

  query(text, params) {
    return new Promise((resolve, reject) => {
      try {
        const result = pool.query(text, params);
        return resolve(result);
      } catch (error) {
        return reject(error);
      }
    });
  },
};

// controller for a table
const Table = {
  getOne: async (id) => {
    return await db.query('SELECT * FROM table WHERE id=$1', [id]);
  },
}

这很好用，可以通过消耗try/catch块中的一部分来处理，并且无论查询返回结果还是错误都可以使用.现在我该如何在打字稿中键入这些内容?我尝试这样做:

This works fine and could be processed by consuming part in a try/catch block and it works whether the query returns a result or an error. Now how should I type these in typescript? I tried doing this:

import { Pool } from 'pg';

const pool = new Pool({
  connectionString: 'process.env.DB_CONNECTION',
});

export default {

  query(text: string, params: any[]) {
    return new Promise((resolve, reject) => {
      try {
        const result = pool.query(text, params);
        return resolve(result);
      } catch (error) {
        return reject(error);
      }
    });
  },
};

// controller
import { QueryResult } from 'pg';

const Table = {
  getOne: async (id: string) => {
    return await db.query('SELECT * FROM table WHERE id=$1', [id]) as QueryResult;
  },
}

现在，可以编译了，但是有一些我没有得到的东西.首先，始终将这些返回类型转换为'as'是非常多余的.我不应该能够像这样getOne: async (id: string): Promise<QueryResult> => {...}那样声明返回类型吗?那么，如果诺言被拒绝，会发生什么呢?那不再是QueryResult类型.我已经尝试阅读有关node-postgres和TypeScript函数类型声明的文档，但是却一无所获.我应该怎么做?也可能我也应该开始学习声明文件.

Now, this compiles, but there are couple things I don't get. First, it is quite redundant to always cast these return types with 'as'. Shouldn't I be able to declare the return type somehow like this getOne: async (id: string): Promise<QueryResult> => {...}? Then, what would happen, if the promise rejected? That isn't a QueryResult type anymore afaik. I have tried to read the documentations about node-postgres and TypeScript function type declarations, but I am getting nowhere. How I should do these? Also probably I should start learning declaration files too.

推荐答案

异步函数隐式返回promise

async functions implicitly return promises

示例:

// Declare async function
async function getRandomNumberAsync(max: number): Promise<number> {
  return Math.floor(Math.random() * Math.floor(max));
}

// Call it (errors are handled with a try/catch)
try {
  const result = await getRandomNumberAsync(100);
  console.log(result);
} catch (e) {
  console.error("something went wrong");
}

异步/等待只是语法糖(在后台，异步/等待使用Promises).该代码基本上等同于上面的代码

async/await is just syntax sugar (behind the scenes, async/await use Promises). This code is basically equivalent to the above code

function getRandomNumberAsync(max: number): Promise<number> {
  return Promise.resolve(Math.floor(Math.random() * Math.floor(max)));
}

getRandomNumberAsync(100).then(result => {
  console.log(result);
}).catch(e => {
  console.error("something went wrong");
})

我可以看到在您的代码中，您正在使用return await，这是多余的.甚至还有 eslint规则防止这种情况

I can see that in your code, you're using return await which is redundant. There's even an eslint rule to prevent this

您的代码应如下所示

const Table = {
  getOne: async (id: string): Promise<QueryResult> => {
    return db.query('SELECT * FROM table WHERE id=$1', [id]);
  },
}

// "getOne" should be called like this
try {
  const result = await Table.getOne("YOUR_ID");
  // handle result
} catch (e) {
  // handle error
}

除非您要处理getOne

它应该看起来像这样

const Table = {
  getOne: async (id: string): Promise<QueryResult | string> => {
    try {
      return await db.query("SELECT * FROM table WHERE id=$1", [id]);
    } catch (e) {
      return "something went wrong";
    }
  },
}

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