Getting empty array in nodejs

Question

I am posting value But I am getting empty array . I know its node asynchronous problem . But I don't know how do i solve this. I have refer this following link:

How do I return the response from an asynchronous call?

But I could not able to understand . Kindly help me to understand promises and how do i use that in my code.

router.post('/inspection_list', function (req, res) {
    var id = req.body.project_id;
    console.log(id)
// res.send("ok")
    db.inspection.findOne({'_id':id},(err,response)=>{
        if(err){
            console.log("error");
        }
        else{
            console.log("Data")
            var inspection = [];
            var data = response.inspection_data;
      var f =  data.map(function (item) { 
                var fielduser = item.fielduser_id
                db.fielduser.findOne({'_id': mongoose.Types.ObjectId(fielduser)},(err,user)=>{
                    console.log(user.owner_name);
                    console.log(item.inspection_name)
                    inspection.push({inspection_name:item.inspection_name,field_user_name : user.owner_name})


                })
                });
console.log(inspection) // Here am getting empty value
           // setTimeout(function(){ console.log(inspection) }, 5000); my timeout code


        }
    })
});

What is the output of console.log(user.owner_name); and console.log(item.inspection_name) ? — eduPeeth
– eduPeeth, Commented Jul 6, 2018 at 7:18
Ya am getting the user name and inspection name in that.. if I set timeout function for console.log am getting the value — Vishnu
– Vishnu, Commented Jul 6, 2018 at 7:21
How about if you don't set time out? Can you post the time out code snippet as well? — eduPeeth
– eduPeeth, Commented Jul 6, 2018 at 7:23

pr0p · Accepted Answer · 2018-07-06 09:20:53Z

2

router.post('/inspection_list', async function (req, res) {
    var id = req.body.project_id;
    try{
        var response = await db.inspection.findOne({'_id':id})
        var inspection = [];
        var data = response.inspection_data;
        for ( var i = 0; i<data.length; i++){
            var item = data[i]
            var fielduser = item.fielduser_id
            var user = await db.fielduser.findOne({'_id': mongoose.Types.ObjectId(fielduser)})
            inspection.push({inspection_name:item.inspection_name,field_user_name : user.owner_name})
       }
    }
    catch(err){
        throw err
    }
})

This uses async and await, you can use it if you are using node version >=7.6

Also note the following:

router.post('/inspection_list', async function (req, res)

Handling each error seperately

router.post('/inspection_list', async function (req, res) {
    var id = req.body.project_id;
    try{
        var response = await db.inspection.findOne({'_id':id})
    }
    catch(err){
        // handle error here
        throw err
    }
    var inspection = [];
    var data = response.inspection_data;
    for ( var i = 0; i<data.length; var item = data[i]
        var fielduser = item.fielduser_id
        try{
            var user = await db.fielduser.findOne({'_id': mongoose.Types.ObjectId(fielduser)})
        }
        catch(err){
             // handle error
        }            
        inspection.push({inspection_name:item.inspection_name,field_user_name : user.owner_name})
   }

})

edited Jul 6, 2018 at 9:20

answered Jul 6, 2018 at 8:06

pr0p

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11 Comments

pr0p Over a year ago

Check the query "router.post('/inspection_list', async function (req, res) "

pr0p Over a year ago

add async there

pr0p Over a year ago

I'll block text the async maybe then you'll get it

Vishnu Over a year ago

am getting empty only

pr0p Over a year ago

Let us continue this discussion in chat.

|

Milan Velebit · Accepted Answer · 2018-07-06 08:57:07Z

0

Using mongoose would be the easy way out, it returns Promises for all query and save functions, so you'd simply do: YourModel.findOne({params}).then(() => {...})

If you're unable to do that, in your case, a 'promisified' example would be:

var findAndFillArray = (project_id) => new Promise((resolve) => {
    .... your previous code here .... 
    inspection.push({inspection_name:item.inspection_name,field_user_name : 
      user.owner_name})
    if (data.length === inspection.length){  // Or some other preferred condition
       resolve(inspection);
    }
})

Then you'd call this function after you get the id, like any other function:

var id = req.body.project_id;
findAndFillArray(id).then((inspection_array) => {
    res.send(inspection_array) // Or whatever
})

Now, map and all list functions are synchronous in JS, are you sure the error is due to that?

edited Jul 6, 2018 at 8:57

answered Jul 6, 2018 at 7:43

Milan Velebit

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3 Comments

eduPeeth Over a year ago

can't there be scenario where data.length === inspection.length doesn't hold? How will it be resolved then? And that's a valid scenario I think.

Milan Velebit Over a year ago

@eduPeeth I just placed a placeholder, he could whichever condition he wants, I'll edit the code with the comment

Milan Velebit Over a year ago

@eduPeeth Might even pass a reject param and add a reject condition in case some values are missing, now I have no actual knowledge of what the code should act like so I'll leave that up to the author :)

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