Question

我正在学习在 NodeJS 中集成 Sequalize 。我写了两个查询。第一个在数据库中创建一个产品条目，另一个在数据库表中检索所有条目。我已将创建查询放在检索查询之前，但是检索查询会在执行创建查询之前给出结果。

任何人都可以解释我在做什么错以及如何预防吗？我已经在下面粘贴了代码和结果。

以下是脚本：

const express = require('express');
const app = express();
const bodyParser = require('body-parser');
const path = require('path');
const Sequelize = require("sequelize");
const sequelize = new Sequelize('practiseapp','root','Current-Root-Password',{
    dialect:'mysql',
    host:'localhost'
});
const product = require("./models/product");
app.use(bodyParser.urlencoded({extented:false}));

sequelize.sync().then(result =>{
        console.log("Success");
}).catch(err=>{
    console.log("Error in connection mysql");
});


const addProduct = (req,res,next)=>{
    product.create({
    title:"Dhruv",
    imageUrl: "asdasdwadasd",
    description : 'How u doin'
}).then(function(user){
    console.log("Product Created");
}).catch(function(err){
    console.log("cant create");
});
}
addProduct();

const findProduct = (req,res,next)=>{
    product.findAll().then(users => {
    console.log("Reached find all");
    console.log("All users:", JSON.stringify(users, null, 4));
});
}
findProduct();

app.listen(3000);

这是执行的输出：

[nodemon] starting `node app.js`
body-parser deprecated undefined extended: provide extended option app.js:10:20
Executing (default): SELECT `id`, `title`, `imageUrl`, `description`, `createdAt`, `updatedAt` FROM `products`
AS `product`;
Executing (default): CREATE TABLE IF NOT EXISTS `products` (`id` INTEGER NOT NULL auto_increment , `title` VARCHAR(255), `imageUrl` VARCHAR(255) NOT NULL, `description` VARCHAR(255) NOT NULL, `createdAt` DATETIME NOT NULL, `updatedAt` DATETIME NOT NULL, PRIMARY KEY (`id`)) ENGINE=InnoDB;
Executing (default): INSERT INTO `products` (`id`,`title`,`imageUrl`,`description`,`createdAt`,`updatedAt`) VALUES (DEFAULT,?,?,?,?,?);
Reached find all
All users: [
    {
        "id": 1,
        "title": "Dhruv",
        "imageUrl": "asdasdwadasd",
        "description": "How u doin",
        "createdAt": "2019-06-05T17:39:43.000Z",
        "updatedAt": "2019-06-05T17:39:43.000Z"
    },
    {
        "id": 2,
        "title": "Dhruv",
        "imageUrl": "asdasdwadasd",
        "description": "How u doin",
        "createdAt": "2019-06-05T17:44:24.000Z",
        "updatedAt": "2019-06-05T17:44:24.000Z"
    },
    {
        "id": 3,
        "title": "Dhruv",
        "imageUrl": "asdasdwadasd",
        "description": "How u doin",
        "createdAt": "2019-06-05T17:44:34.000Z",
        "updatedAt": "2019-06-05T17:44:34.000Z"
    }
]
Executing (default): SHOW INDEX FROM `products`
Success
Product Created

Answer 1

由于Node.js本质上是异步的，因此正常的执行流程将不起作用。

您可以通过使用承诺或回调来实现上述用例。

这些将帮助您控制流程，即仅在第一个函数完全执行后才执行第二个函数。

Answer 2

只需将 findProduct（）函数保留在 addProduct 的主体中即可。
其他方法也请先尝试并回复。

   const addProduct = (req,res,next)=>{
        product.create({
        title:"Dhruv",
        imageUrl: "asdasdwadasd",
        description : 'How u doin'
    }).then(function(user){
        console.log("Product Created");
        findProduct();
    }).catch(function(err){
        console.log("cant create");
    });
    }
    addProduct();
    const findProduct = (req,res,next)=>{
        product.findAll().then(users => {
        console.log("Reached find all");
        console.log("All users:", JSON.stringify(users, null, 4));
    });
    }

Answer 3

您的查询是异步函数。如果查找查询在创建之前返回，仅仅是因为其处理速度很快。如果要确保在第一个完成后执行第二个，则应在add回调中调用它。例如：

product.create({
    title: "Dhruv",
    imageUrl: "asdasdwadasd",
    description: 'How u doin'
}).then(function(user){
    console.log("Product Created");

    product.findAll().then(products => {
        console.log("Reached find all");
        console.log("All products:", JSON.stringify(users, null, 4));
    }).catch(function(err){
        console.log("cant find");
    });
}).catch(function(err){
    console.log("cant create");
});

Answer 4

这是另一种方法。

   const addProduct = (req,res,next)=>{
        product.create({
        title:"Dhruv",
        imageUrl: "asdasdwadasd",
        description : 'How u doin'
    }).then(function(user){
        console.log("Product Created");
        return product.findAll().then(users => {
                console.log("Reached find all");
                console.log("All users:", JSON.stringify(users, null, 4));
            });

    })
    .then(data => {
        console.log(data)
    })
    .catch(function(err){
        console.log("cant create");
    });
    }
    addProduct()

Nodejs如何决定先执行哪个功能？

4 个答案: