如何在节点js中执行forloop

Question

Acoording to the data available ui should get 2 reults but getting only one since i put res.send in the looop so it is getting ended ,can anyone help me out please.......

exports.getrequestsdetails = function(req, res) {
    var params = req.params;
    console.log(params)
    var record = db.collection('requests');
    var item = {
        "sent_id": params.id,
        "status": 1
    }
    record.find(item).toArray((err, result) => {
        if (err) {
            return
        }
        if (result) {
            for (var i in result) {
                var id = result[i].recieved_id;
                var profile = db.collection('profile');
                profile.find({
                    '_id': new ObjectId(id)
                }).toArray((err, resp) => {
                    if (err) {
                        return
                    }
                    if (resp) {
                        console.log(resp);
                    } else {}
                });
            }
            res.send(resp);
        } //end of if loop
        else {
            response = {
                status: 'fail',
                data: []
            };
        }

    });

}

Answer 1

You can send only one response back to a request.

Define a variable outside the for loop, append records to it and then send it after the for loop has ended.

exports.getrequestsdetails = function(req, res) {
var params = req.params;
console.log(params)
var record = db.collection('requests');
var item = {
    "sent_id": params.id,
    "status": 1
}

var resList = [];

record.find(item).toArray((err, result) => {
        if (err) {
            return
        }
        if (result) {
            for (var i in result) {
                var id = result[i].recieved_id;
                var profile = db.collection('profile');
                profile.find({
                    '_id': new ObjectId(id)
                }).toArray((err, resp) => {
                        if (err) {
                            return
                        }
                        if (resp) {
                           console.log(resp);
                           resList[i] = resp;
                        }
                        else{
                      }
                });
            }
        }//end of if loop
        else {
             resList = {
                status: 'fail',
                data: []
              };
         }
        res.send(resList);
       });

Answer 2

You can push all the resp in list array and send after completing loop .

Like this:

    exports.getrequestsdetails = function(req, res) {
    var params = req.params;
    console.log(params);

    var record = db.collection('requests');
    var item = {
        "sent_id": params.id,
        "status": 1
    };

    record.find(item).toArray((err, result) => {
        if (err) {
            return err;
        }
        if (result) {
            var list = [];
            for (var i in result) {
                var id = result[i].recieved_id;
                var profile = db.collection('profile');
                profile.find({
                    '_id': new ObjectId(id)
                }).toArray((err, resp) => {
                    if (err) {
                        return err;
                    }
                    else{
                        list.push(resp);
                        console.log(resp);
                        if(i===result[result.length-1]){
                             res.send(list);
                        }
                    }
                });
            }

        } //end of if loop
        else {
            response = {
                status: 'fail',
                data: []
            };
        }

    });
};

Hope this work for you

Answer 3

Don't use for loop in asynchronous mode. Use async module instead like below.

var async = require('async');
exports.getrequestsdetails = function (req, res) {
    var params = req.params;
    console.log(params)
    var record = db.collection('requests');
    var item = {
        "sent_id": params.id,
        "status": 1
    }
    record.find(item).toArray(function (err, result) {
        if (err) {
            return
        }
        if (result) {
            var list = [];
            async.each(result, function (item, cb) {
                var id = item.recieved_id;
                var profile = db.collection('profile');
                profile.findOne({
                    '_id': new ObjectId(id)
                }, function (err, resp) {
                    if (err) {
                        return cb();
                    }
                    if (resp) {
                        list.push(resp);
                        console.log(resp);
                        return  cb();
                    }
                    return cb();
                });
            }, function (err) {
                res.send(list);
            });
        }//end of if loop
        else {
            response = {
                status: 'fail',
                data: []
            };
        }

    });

}

Answer 4

The problem is in getting the profiles. You are using mongodb's find which is asynchronous . Therefore in your for cycle you start fetching the profiles, but then you send out the res.send well before the fetching of the profiles is finished.

The call back from profile.find(... will be executed after the res.send . Apart from this, the resp variable is inside the find callback and you are trying to res.send it outside.

To deal with this, either you use async or promises . See the below code that uses promises.

var Promise = require('bluebird')

exports.getrequestsdetails = function(req, res) {
    var params = req.params;
    console.log(params)
    var record = db.collection('requests');
    var item = {
        "sent_id": params.id,
        "status": 1
    }

    record.find(item).toArray((err, result) => {
        if (err) {
            return
        }
        if (result) {

            var profiles_to_get = []
            var profiles = []

            for (var i in result) {
                var id = result[i].recieved_id;
                profiles_to_get.push(get_profile(id, profiles))
            }

            Promise.all(profiles_to_get)
                .then(() => {
                    res.send(profiles);
                })
        } //end of if loop
        else {
            response = {
                status: 'fail',
                data: []
            };
        }

    });

    function get_profile (id, profiles) {
        return new Promise(function (resolve, reject) {
            var profile = db.collection('profile');
                profile.find({
                    '_id': new ObjectId(id)
                }).toArray((err, resp) => {
                    if (err) {
                        reject(err)
                        return
                    }
                    if (resp) {
                        profiles.push(resp)
                        resolve()
                    } else {
                        reject()
                    }
                });
        })
    }

}

How this works is that it creates a list of profiles to find and stores it in the var profiles_to_get = [] . The you use Promise.All(profiles_to_get) which will let you do stuff after all the profiles have been fetched.

Answer 5

您可以将所有列表添加到数组中，最后在循环后发送数据