Web User Web User - 5 months ago 35
Node.js Question

How to update MongoDB documents with arrays of sub-documents

I am working with a MongoDB database whose collections model classes, students, subjects, and [academic] performance. Below are the Mongoose based schema and models:

var mongoose = require('mongoose');
var Schema = mongoose.Schema;
var ObjectId = Schema.Types.ObjectId;

// SUBJECT collection
var subjectSchema = new Schema({
name : { type: String, required: true },
category : { type: String, required: true }
});
var Subject = mongoose.model('Subject', subjectSchema);

// STUDENT collection
var studentSchema = new Schema({
name : { type: String, required: true },
grade : { type: Number, required: true }
});
var Student = mongoose.model('Student', studentSchema);

// PERFORMANCE collection
var performanceSchema = new Schema({
subjectId : { type: ObjectId, ref: Subject.modelName, required: true },
score : { type: Number, required: true },
maximum : { type: Number, required: true },
grade : { type: String, required: true }
});
var Performance = mongoose.model('Performance', performanceSchema);

// *Note*: This is just to use as a sub-document schema, and not as a collection
var classStudentSchema = new Schema({
studentId : { type: ObjectId, ref: Student.modelName, required: true },
performance : [performanceSchema]
}, { _id: false });

// CLASS collection
var classSchema = new Schema({
name : { type: String, required: true },
scores : [classStudentSchema]
});
var Class = mongoose.model('Class', classSchema);


The
class
collection's documents are the most complex of the lot; an example document would be:

{
"_id" : ObjectId("57758f15f68da08c254ebee1"),
"name" : "Grade 5 - Section A",
"scores" : [{
"studentId" : ObjectId("5776bd36ffc8227405d364d2"),
"performance": [{
"subjectId" : ObjectId("577694ecbf6f3a781759c54a"),
"score" : 86,
"maximum" : 100,
"grade" : "B+"
}, {
"subjectId" : ObjectId("5776ffe1804540e29c602a62"),
"score" : 74,
"maximum" : 100,
"grade" : "A-"
}]
}, {
"studentId" : ObjectId("5776bd36ffc8227405d364d5"),
"performance": [{
"subjectId" : ObjectId("577694ecbf6f3a781759c54a"),
"score" : 94,
"maximum" : 100,
"grade" : "A"
}, {
"subjectId" : ObjectId("5776ffe1804540e29c602a62"),
"score" : 81,
"maximum" : 100,
"grade" : "A"
}]
}]
}


I was able to retrieve an existing class document and add a student to it's scores using the following code:

Class.findOne({ name: 'Grade 5 - Section A' }, function(err, class) {
if (err) throw err;
Student.findOne({ name: 'John Doe' }, function(err, student) {
if (err) throw err;
class.scores.push({
studentId: student.id
});
};
});


But how do I add/update/delete that particular student's performance? I need to be able to interact with the
class
collection in the following ways:


  • Retrieve the scores for all students, or for a specific student (retrieve specific element in the
    scores
    array)

  • Add/ update/ delete a specific student's score, for a specific subject (in case of update or delete, retrieve a specific element in the
    scores[n].performance
    array; for add, append to the same array.


Tim Tim
Answer

There are a few way to do this I'll answer point by point

Retrieve the scores for all students, or for a specific student (retrieve specific element in the scores array)

Class.findOne({ name: 'Grade 5 - Section A'})
     .populate('scores.studentId')
     .exec(function(err, class) {
       if (err) throw err;
       //now class.scores.studentId becomes ObjectStudent
       //hence you have all scores for all students
});

Add/ update/ delete a specific student's score, for a specific subject (in case of update or delete, retrieve a specific element in the scores[n].performance array; for add, append to the same array.

Class.findOneAndUpdate({name: 'Grade 5 - Section A'
                        ,'scores.studentId': ObjectId('5776bd36ffc8227405d364d2')
                        , 'scores.performance.subjectId' : ObjectId('577694ecbf6f3a781759c54a')}
                        , {$set: {scores.performance. score: 50}}
                        , function(err, data) {
           if (err) throw err
    });

I hope that helps