javascript - 当发布到数据库时，我收到 "Can' t set headers after they are sent error”

Question

在这个问题中，我发布了从开始到结束进行销售的完整数据流，因为我不知道错误在哪里。在我的应用程序中，我在 Checkout 组件中调用了一个名为 handlePay() 的函数，该函数又调用了一个名为 makeSale() 的 Action 创建器。 makeSale() 然后向 router.js 中的服务器发出 POST 请求，服务器将使用 mongoose 在数据库中处理此次销售。控制台的错误显示为

"/Users/marcushurney/Desktop/P.O.S./node_modules/mongodb/lib/utils.js:98 process.nextTick(function() { throw err; }); ^

错误:发送后无法设置 header 。"

我不确定我的代码中是否存在此错误，该代码与 router.js 中的数据库或前端的其他地方进行通信。前端组件称为 Checkout.jsx，处理销售的函数是 handlePay()，其关联的 Action 创建器是 makeSale()。

Checkout.jsx

handlePay: function() {

        var props = {
            user_id: this.props.activeUser._id, //This sale will belong to the user that is logged in (global state)
            items: [], //All the items in the cart will be added to the sale below (global state)
            total: this.props.cartTotal //Total price of the sale is drawn from the global state
        }


        this.props.cart.map((product) => {
            var item = {};
            item.name = product.name;
            item.product_id = product._id;
            item.cartQuantity = product.cartQuantity;
            item.priceValue = product.price;
            props.items.push(item);
        });

        var jsonProps = JSON.stringify(props); //converts properties into json before sending them to the server

        this.props.makeSale(jsonProps); 
    }

actions/index.js

export function makeSale(props) {

    var config = {headers: {'authorization' : localStorage.getItem('token')}};

    var request = axios.post('/makeSale', props, config); //This will store the sale in the database and also return it

    return {
        type: MAKE_SALE,
        payload: request //Sends sale along to be used in sale_reducer.js
    };

}

router.js

    //Adds a new sale to the database
    //Getting error "can't set headers after they are sent"

    app.post('/makeSale', function(req, res, next){

        var sale = new Sale();
        sale.owner = req.body.user_id;
        sale.total = req.body.total;

        req.body.items.map((item)=> {

            //pushs an item from the request object into the items array           contained in the sale document

            sale.items.push({
                item: item.product_id,
                itemName: item.name,
                cartQuantity: parseInt(item.cartQuantity), //adds cartQuantity to sale
                price: parseFloat(item.priceValue)
            });


            Product.findById(item.product_id)
            .then((product) => {

                //finds the item to be sold in the database and updates its quantity field based on the quantity being sold

                product.quantity -= item.cartQuantity; 

                //resets the product's cartQuantity to 1

                product.cartQuantity = 1;

                product.save(function(err) {
                    if (err) { 
                        return next(err); 
                    } else {
                        return next();
                        // return res.status(200).json(product);
                    }
                });
            }, (error) => {
              return next(error);
            });
        });

        //gives the sale a date field equal to current date

        sale.date = new Date();

        //saves and returns the sale

        sale.save(function(err) {
            if (err) { return next(err); }
            return res.status(200).json(sale); //Returns the sale so that it can be used in the sale_reducer.js
        });

    });

这是 Mongoose 的销售模型 --> sale.js

var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var SalesSchema = new Schema({
    owner: { type: Schema.Types.ObjectId, ref: 'User'},
    total: { type: Number, default: 0},
    items: [{
        item: { type: Schema.Types.ObjectId, ref: 'Product'},
        itemName: { type: String, default: "no name provided"},
        cartQuantity: { type: Number, default: 1 },
        price: { type: Number, default: 0 }
    }],
    date: Date
});

module.exports = mongoose.model('Sale', SalesSchema);

Answer 1

Product.findById 是异步的，最终会多次调用 next()，这(很可能)会导致多次尝试发送响应，这将导致您看到的错误。

通常(或总是，可能)，您只想为每个中间件调用一次 next()。

试试这个:

"use strict";

app.post('/makeSale', function(req, res, next){

    var sale = new Sale();
    sale.owner = req.body.user_id;
    sale.total = req.body.total;

    return Promise.all(req.body.items.map((item) => {

        // pushs an item from the request object into the items array contained in the sale document
        sale.items.push({
            item: item.product_id,
            itemName: item.name,
            cartQuantity: parseInt(item.cartQuantity, 10), // adds cartQuantity to sale
            price: parseFloat(item.priceValue)
        });

        return Product.findById(item.product_id).then((product) => {

            //finds the item to be sold in the database and updates its quantity field based on the quantity being sold

            product.quantity -= item.cartQuantity; 

            //resets the product's cartQuantity to 1
            product.cartQuantity = 1;
            return product.save();
        });
    }))
    .then(() => {
        //gives the sale a date field equal to current date
        sale.date = new Date();

        //saves and returns the sale
        return sale.save();
    })
    .then(() => {
        return res.status(200).json(sale);
    })
    .catch(next);
});