迭代时使Mongoose中的Node.js代码同步

Question

I am learning Node.js; due to asynchronous of Node.js I am facing an issue:

domain.User.find({userName: new RegExp(findtext, 'i')}).sort('-created').skip(skip).limit(limit)
        .exec(function(err, result) {

                for(var i=0;i<result.length;i++){
                    console.log("result is ",result[i].id);
                    var camera=null;
                    domain.Cameras.count({"userId": result[i].id}, function (err, cameraCount) {
                        if(result.length-1==i){
                            configurationHolder.ResponseUtil.responseHandler(res, result, "User List ", false, 200);
                        }
                    })
                }
            })

I want to use result in Cameras callback but it is empty array here, so is there anyway to get it?

And this code is asynchronous, is it possible if we make a complete function synchronous?

Answer 1

@jmingov is right. You should make use of the async module to execute parallel requests to get the counts for each user returned in the User.find query.

Here's a flow for demonstration:

var Async = require('async'); //At the top of your js file.

domain.User.find({userName: new RegExp(findtext, 'i')}).sort('-created').skip(skip).limit(limit)
        .exec(function(err, result) {

            var cameraCountFunctions = [];

            result.forEach(function(user) {

               if (user && user.id)
               {
                    console.log("result is ", user.id);
                    var camera=null; //What is this for?

                    cameraCountFunctions.push( function(callback) {

                        domain.Cameras.count({"userId": user.id}, function (err, cameraCount) {

                                if (err) return callback(err);

                                callback(null, cameraCount); 
                        });
                    });
               }
            })

            Async.parallel(cameraCountFunctions, function (err, cameraCounts) {
                    console.log(err, cameraCounts);
                    //CameraCounts is an array with the counts for each user.
                    //Evaluate and return the results here.
            }); 

        });

Answer 2

Try to do async programing allways when doing node.js, this is a must. Or youll end with big performance problems.

Check this module: https://github.com/caolan/async it can help.

Here is the trouble in your code:

domain.Cameras.count({
    "userId": result[i].id
}, function(err, cameraCount) {

    // the fn() used in the callback has 'cameraCount' as argument so
    // mongoose will store the results there.

    if (cameraCount.length - 1 == i) { // here is the problem
        //  result isnt there it should be named 'cameraCount'   
        configurationHolder.ResponseUtil.responseHandler(res, cameraCount, "User List ", false, 200);
    }
});