Nodejs +Express+Mongoose初学者问题:

*所以我遇到了这个问题，我有一个类别数组(服装类别)。对于每个类别，我想从数据库中获取结果。所以我做了一个正常人会做的事。我使用了一个 for 循环，获取产品，存储在一个数组中，然后获取下一个产品，存储在同一个数组中等等......(男性和女性的过程相同)。现在我想用数据呈现我的 View ，但由于 Node js 的异步性质，它不可访问。我完全理解。所以我正在寻找的是我的问题的替代/解决方案 *

我的 express 代码更好地解释了我的痛苦。请看:

//INDEX PAGE
router.get('/', (req, res, next) => { //anonymous callback function
let allCategories;
let womenFashion = [],
    menFashion = [];
Clothing.groupByBodyPart(function(err, categories) {
    if (categories) {
        allCategories = categories.slice(0);
        for (let i = 0; i < allCategories.length; i++) { //looping
            let category = allCategories[i]._id; //gives a category, eg.,footwear,bottomwear
            Clothing.getCategoryWise(category, 'M', function(err, products) { //products here will be an array of objects
                if (products) {
                    menFashion[i] = products.slice(0); //storing products into an array for future use
                    console.log(menFashion[i]); //accessible here one at a time Eg.,[{slippers},{shoes}]
                }
            });
            Clothing.getCategoryWise(category, 'F', function(err, products) {
                if (products) {
                    womenFashion[i] = products.slice(0); //same as above
                    console.log(womenFashion[i]); //same as above
                }
            });
        }
    }
    console.log(menFashion[0]); // not accessible here, so I can't render my page 
    res.render('index.pug', {
        allCategories,
        menFashion,
        womenFashion
    }); //won't work as menFashion and womenFashion aren't available
});
});

这里是 mongoose 静态函数:

//get categorywise  products
clothingSchema.statics.getCategoryWise = function(bodyPart,gender,callback){
Clothing.aggregate([
  { $match: {'category.bodyPart': bodyPart,
            'category.gender': gender
            }
  },
  { $group: {_id: "$category.type"  }
  },
  { $sort: {_id: 1 }
  }
])
.exec((err,products)=>{
    if(err){
        return callback(err); 
    }else if(!products){
        let err = new Error('No Product Found!');
        err.status = 401;
        return callback(err);
    }
    return callback(null,products);
});
}

仅作记录

一切都很好，我只是在呈现我的页面时遇到问题，因为 menFashion 和 womenFashion 数组在回调之外不可访问。

提前致谢:)

更新:

我自己解决了，但仍然感谢大家(特别是@faiz)

我的解决方案基本上包括嵌套:

//INDEX PAGE
router.get('/',(req,res,next)=>{ //anonymous callback function
let allCategories;
let womenFashion = [], menFashion = [];
Clothing.groupByBodyPart(function(err,categories){
    if(categories){
        allCategories = categories.slice(0);
        for(let i = 0; i < allCategories.length; i++){ //looping
            let category = allCategories[i]._id;        //gives a category, eg.,footwear,bottomwear
            Clothing.getCategoryWise(category,'M',function(err,products){ //products here will be an array of objects
                if(products){
                    menFashion.push(products);
                    menFashion[i] = products.slice(0); //storing products into an array for future use
                    //console.log(menFashion[i]);       //accessible here on at a time Eg.,[{slippers},{shoes}]
                }
                Clothing.getCategoryWise(category,'F',function(err,products){
                    if(products){
                        womenFashion[i] = products.slice(0);    //same as above
                        //console.log(womenFashion[i]);         //same as above
                    }
                    if(i == allCategories.length-1){
                        console.log('men',menFashion); //everything accessible
                        console.log('men',menFashion); //everything accessible
                        res.render('index.pug',{allCategories,menFashion,womenFashion}); //tadaaaaaaaa
                    }
                }); 
            });                 
        }               
    }
}); 
});

最佳答案

你可以使用这样的东西。

我使用了两个 Promise.all 调用来确保您有两个可以使用的结果。您也可以使用一个 Promise.all

router.get('/', (req, res, next) => { //anonymous callback function
    let allCategories;
    let womenFashion = [],
        menFashion = [];
    Clothing.groupByBodyPart(function (err, categories) {
        if (categories) {
            allCategories = categories.slice(0);
            const menPromises = [];
            const womenPromises = [];
            for (let i = 0; i < allCategories.length; i++) { //looping
                let category = allCategories[i]._id; //gives a category, eg.,footwear,bottomwear
                menPromises.push(
                    new Promise((resolve, reject) => {
                        Clothing.getCategoryWise(category, 'M', function (err, products) { //products here will be an array of objects
                            if (products) {
                                menFashion[i] = products.slice(0); //storing products into an array for future use
                                resolve(menFashion[i]);
                                console.log(menFashion[i]); //accessible here one at a time Eg.,[{slippers},{shoes}]
                            }
                        })
                    })
                );
                womenPromises.push(
                    new Promise((resolve, reject) => {
                        Clothing.getCategoryWise(category, 'F', function (err, products) { //products here will be an array of objects
                            if (products) {
                                womenFashion[i] = products.slice(0); //storing products into an array for future use
                                resolve(womenFashion[i]);
                                console.log(womenFashion[i]); //accessible here one at a time Eg.,[{slippers},{shoes}]
                            }
                        })
                    })
                );
            }

            Promise.all([Promise.all(menPromises), Promise.all(womenPromises)]).then(([menResults, womenResults]) => {
                console.log(menFashion[0]); // not accessible here, so I can't render my page 
                res.render('index.pug', {
                    allCategories,
                    menFashion,
                    womenFashion
                }); //won't work as menFashion and womenFashion aren't available
            });
        }
    });
});

关于node.js - 使用 express 循环 mongoose 模式函数，将数据收集到一个数组中，最后用所有数据呈现页面，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/48848536/