How to fix "Result undefined" in MongoDB Stitch function

Question

I'm creating Stitch Functions in MongoDB and getting result undefined instead of double.

I'm developing an iOS App, using MongoDB database. I'm creating Stitch Functions, and using callFunction(withName:withArgs:_:) method. I write a function to calculate an average morning value. I want to return the morning value to app. Here is the code below.

exports = function(DAY,MONTH){
    var total = 0.0;
    var count = 0.0;
    var morning = 0.0;

    var collection = context.services.get("mongodb-atlas").db("database_name").collection("collection_name");
    var docs = collection.find({month: { $eq: MONTH },
    day: { $eq: DAY },
    hour: { $gte: 8 },
    hour: { $lt: 13 }
    }).toArray().then((data) => {
        data.forEach((el) =>{
            total = total +  el.value;
            count = count + 1.0; 
        });
        morning = total/count;
        console.log("morning");
        console.log(morning);
        return {morning};
    })
    .catch((error) => {
        console.log(error);
        return {morning};
    });
};

"""output"""

morning 869.5729166666666

result: { "$undefined": true } result (JavaScript): EJSON.parse('{"$undefined":true}')

"""-end of output"""

I'm trying to return morning value which is double but, it returns BSONUndefined. And when I try to reach result from iOS app, I get """ morning: BSONUndefined() """ But before the return statement, it prints the morning value to stitch console correctly.

score 2 · Answer 1 · answered Aug 13 '19 at 18:28

use the return statement before the MongoDB find() query this way

exports = function(DAY,MONTH){
    var total = 0.0;
    var count = 0.0;
    var morning = 0.0;

    var collection = context.services.get("mongodb-atlas").db("database_name").collection("collection_name");
    return collection.find({month: { $eq: MONTH },
    day: { $eq: DAY },
    hour: { $gte: 8 },
    hour: { $lt: 13 }
    }).toArray().then((data) => {
        data.forEach((el) =>{
            total = total +  el.value;
            count = count + 1.0; 
        });
        morning = total/count;
        console.log("morning");
        console.log(morning);
        return {morning};
    })
    .catch((error) => {
        console.log(error);
        return {morning};
    });
};

score 0 · Answer 2 · answered Jul 15 '19 at 06:08

you are not written the collection, {which is sending the $undefined:true}

Solution 1 Return collection.find result

return collection.find({month: { $eq: MONTH },
    day: { $eq: DAY },
    hour: { $gte: 8 },
    hour: { $lt: 13 }
    }).toArray().then((data) => {
        data.forEach((el) =>{
            total = total +  el.value;
            count = count + 1.0; 
        });
        morning = total/count;
        console.log("morning");
        console.log(morning);
        return {morning};
    })
    .catch((error) => {
        console.log(error);
        return {morning};
    });

Solution 2:

Return the docs itself

var docs = collection.find({month: { $eq: MONTH },
    day: { $eq: DAY },
    hour: { $gte: 8 },
    hour: { $lt: 13 }
    }).toArray().then((data) => {
        data.forEach((el) =>{
            total = total +  el.value;
            count = count + 1.0; 
        });
        morning = total/count;
        console.log("morning");
        console.log(morning);
        return {morning};
    })
    .catch((error) => {
        console.log(error);
        return {morning};
    });

return docs

How to fix "Result undefined" in MongoDB Stitch function

2 Answers2