CODEWITHSUNDEEP
javascriptnode.jsmongodbmongoose
dany
dany

Reputation: 1871

To Find the average of a particular type in MongooseJs

I have a MongoDB collection "Marks" as shown below

 _id   Student_id   Subject  Mark
   1    111          AAA      9
   2    111          BBB      5
   3    111          CCC      7
   4    222          AAA      10
   5    222          CCC      6
   6    222          BBB      8

I need to find the average mark scored by student_id=111 in 3 subjects using MONGOOSEJS .I got a solution

var Mark = mongoose.model('mark', new Schema({
  Student_id: Number,
  Subject: String,
  Mark: Number
}));

Mark.aggregate([
    { $group: {
        _id: '$Student_id',
        markAvg: { $avg: '$Mark'}
    }}
], function (err, results) {
    if (err) {
        console.error(err);
    } else {
        console.log(results);
    }
}
);

Output is 

    [ { _id: 222, markAvg: 8 }, { _id: 111, markAvg: 7 } ]

I Want only {_id:111,markAvg:7} when I pass student_id:111 as parameter. Anyone please suggest an answer.

Upvotes: 0

Views: 558

Answers (1)

JohnnyHK
JohnnyHK

Reputation: 311855

You need to add a $match element to the top of your pipeline to filter the documents of the collection to just the ones you want as input to the $group:

Mark.aggregate([
    { $match: { Student_id: 111 } },
    { $group: {
        _id: '$Student_id',
        markAvg: { $avg: '$Mark'}
    }}
], function (err, results) {
    if (err) {
        console.error(err);
    } else {
        console.log(results);
    }
});

Upvotes: 3

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