Improving Mongoose Schema for Course Subscription App - node.js

Question

I am new to mongodb, and playing around with a self-project, where user can subscribe to 3-4 different courses that are predefined. Each course is 1 hour long course everyday, and students can subscribe for either 15, 30 or more days.
App will store information of the students, the course they subscribed for (how many) days and days they were present for the course.
This is my Mongoose Schema.
var mongoose = require('mongoose');
var schemaOptions = {
timestamps: true,
toJSON: {
virtuals: true
}
};
var courseSchema = new mongoose.Schema({
name: String
});
var studentSchema = new mongoose.Schema({
name: String,
email: { type: String, unique: true},
phone: String,
gender: String,
age: String,
city: String,
street: String,
picture: String,
course: [courseSchema],
subscriptionDays: Number,
daysPresent: [Date]
}, schemaOptions);
module.exports = mongoose.model('Student', studentSchema);
Here, course is any of 3-4 courses, one student can subscribe one or more course at same time. subscriptionDays is the number of days they subscribe to, and daysPresent are the days they took the course.
I am not sure if this is the right schema for my project, so far I was able to do this much.
Confusions with the schema are:
When student who is subscribed to two different courses arrives to the
institute, but takes only one class (course), then I do not think this
schema supports the case, for this I thought to modify courseSchema like this,
var courseSchema = new mongoose.Schema({
name: String,
subsriptionDays: Number,
daysPresent: [Date]
});
But, after doing this I am still confused to make changes on the data, like Date has to be inserted into the documents every time student attends for the course.
Second confusion is how will I update the data inside document every day, only the data that has to be inserted on daily basis is the Date inside days.
Can I get some guidance and suggestion from Mongo Experts? TIA

Answer 1

I think that you are basically on the right track with your second thoughts on extending the design. I would really only expand on that by also including a "reference" to the "Course" itself as opposed to just the information embedded on the schema.
As your usage case questions, then they are probably best addressed with a working example:
const async = require('async'),
mongoose = require('mongoose'),
Schema = mongoose.Schema,
ObjectId = Schema.Types.ObjectId;
mongoose.set('debug',true);
mongoose.connect('mongodb://localhost/school');
// Course model
const courseSchema = new Schema({
name: String,
info: String
});
const Course = mongoose.model('Course', courseSchema);
// Student Model
const studentCourseSchema = new Schema({
_id: { type: ObjectId, ref: 'Course' },
name: String,
subscriptionDays: Number,
daysPresent: [Date]
});
const studentSchema = new Schema({
name: String,
email: String,
courses: [studentCourseSchema]
});
studentSchema.index({ "email": 1 },{ "unique": true, "background": false });
const Student = mongoose.model('Student', studentSchema);
function logOutput(content) {
console.log( JSON.stringify( content, undefined, 2 ) )
}
async.series(
[
// Clear collections
(callback) =>
async.each(mongoose.models,
(model,callback) => model.remove({},callback),callback),
// Set up data
(callback) =>
async.parallel(
[
(callback) => Course.insertMany(
[
{ "name": "Course 1", "info": "blah blah blah" },
{ "name": "Course 2", "info": "fubble rumble" }
],
callback),
(callback) => Student.insertMany(
[
{ "name": "Bill", "email": "bill#example.com" },
{ "name": "Ted", "email": "ted#example.com" }
],
callback)
],
callback
),
// Give bill both courses
(callback) => {
async.waterfall(
[
(callback) => Course.find().lean().exec(callback),
(courses,callback) => {
courses = courses.map(
course => Object.assign(course,{ subscriptionDays: 5 }));
let ids = courses.map( c => c._id );
Student.findOneAndUpdate(
{ "email": "bill#example.com", "courses._id": { "$nin": ids } },
{ "$push": {
"courses": {
"$each": courses
}
}},
{ "new": true },
(err, student) => {
logOutput(student);
callback(err);
}
)
}
],
callback
)
},
// Attend one of bill's courses
(callback) => Student.findOneAndUpdate(
{ "email": "bill#example.com", "courses.name": 'Course 2' },
{ "$push": { "courses.$.daysPresent": new Date() } },
{ "new": true },
(err, student) => {
logOutput(student);
callback(err);
}
),
// Get Students .populate()
(callback) => Student.find().populate('courses._id')
.exec((err,students) => {
logOutput(students);
callback(err);
}
)
],
(err) => {
if (err) throw err;
mongoose.disconnect();
}
)
So that should give you a sample of how the operations you ask about actually work.
Add a course to the student Shows addition of a couple of courses where I think you would ideally use $push functionality of MongoDB. To ensure that you are not adding courses that are already there the "query" expression actually excludes selection if they are already present in the courses array. In the example a "list" is passed, so we use $nin but with a single item you would simply use $ne:
{ "email": "bill#example.com", "courses._id": { "$nin": ids } },
{ "$push": { "courses": { "$each": courses } } },
Add an attended date This actually demonstrates a case where you would want to "positionally match" the item within "courses" in order to know which one to update. This is done by providing much like before a condition to "match" as opposed to "exclude" the specific array element. Then in the actual "update" part, we apply the same $push operator so we can append to the "daysPresent"array, but also using the positional $ operator to point to the correct array index position which corresponds to the match condition:
{ "email": "bill#example.com", "courses.name": 'Course 2' },
{ "$push": { "courses.$.daysPresent": new Date() } },
As a bonus there are a few more operations in there showing the relational nature between keeping a list of "Courses" in their own collection with additional information that you probably do not want to embed on each student.
The last operation in the sample actually performs a .populate() to actually pull in this information from the other collection for display.
The whole example has debugging turned on with mongoose.set('debug',true); so you can see what the actual calls to MongoDB are really doing for each operation.
Also get acquainted with the .findOneAndUpdate() method used here, as well as the various "update operators" from the core MongoDB documentation.
Sample output
Mongoose: courses.remove({}, {})
Mongoose: students.remove({}, {})
Mongoose: students.ensureIndex({ email: 1 }, { unique: true, background: false })
(node:10544) DeprecationWarning: Mongoose: mpromise (mongoose's default promise library) is deprecated, plug in your own promise library instead: http://mongoosejs.com/docs/promises.html
Mongoose: courses.insertMany([ { __v: 0, name: 'Course 1', info: 'blah blah blah', _id: 5944d5bc32c6ae2930174289 }, { __v: 0, name: 'Course 2', info: 'fubble rumble', _id: 5944d5bc32c6ae293017428a } ], null)
Mongoose: students.insertMany([ { __v: 0, name: 'Bill', email: 'bill#example.com', _id: 5944d5bc32c6ae293017428b, courses: [] }, { __v: 0, name: 'Ted', email: 'ted#example.com', _id: 5944d5bc32c6ae293017428c, courses: [] } ], null)
Mongoose: courses.find({}, { fields: {} })
Mongoose: students.findAndModify({ 'courses._id': { '$nin': [ ObjectId("5944d5bc32c6ae2930174289"), ObjectId("5944d5bc32c6ae293017428a") ] }, email: 'bill#example.com' }, [], { '$push': { courses: { '$each': [ { daysPresent: [], _id: ObjectId("5944d5bc32c6ae2930174289"), name: 'Course 1', subscriptionDays: 5 }, { daysPresent: [], _id: ObjectId("5944d5bc32c6ae293017428a"), name: 'Course 2', subscriptionDays: 5 } ] } } }, { new: true, upsert: false, remove: false, fields: {} })
{
"_id": "5944d5bc32c6ae293017428b",
"__v": 0,
"name": "Bill",
"email": "bill#example.com",
"courses": [
{
"subscriptionDays": 5,
"name": "Course 1",
"_id": "5944d5bc32c6ae2930174289",
"daysPresent": []
},
{
"subscriptionDays": 5,
"name": "Course 2",
"_id": "5944d5bc32c6ae293017428a",
"daysPresent": []
}
]
}
Mongoose: students.findAndModify({ 'courses.name': 'Course 2', email: 'bill#example.com' }, [], { '$push': { 'courses.$.daysPresent': new Date("Sat, 17 Jun 2017 07:09:48 GMT") } }, { new: true, upsert: false, remove: false, fields: {} })
{
"_id": "5944d5bc32c6ae293017428b",
"__v": 0,
"name": "Bill",
"email": "bill#example.com",
"courses": [
{
"subscriptionDays": 5,
"name": "Course 1",
"_id": "5944d5bc32c6ae2930174289",
"daysPresent": []
},
{
"subscriptionDays": 5,
"name": "Course 2",
"_id": "5944d5bc32c6ae293017428a",
"daysPresent": [
"2017-06-17T07:09:48.662Z"
]
}
]
}
Mongoose: students.find({}, { fields: {} })
Mongoose: courses.find({ _id: { '$in': [ ObjectId("5944d5bc32c6ae2930174289"), ObjectId("5944d5bc32c6ae293017428a") ] } }, { fields: {} })
[
{
"_id": "5944d5bc32c6ae293017428b",
"__v": 0,
"name": "Bill",
"email": "bill#example.com",
"courses": [
{
"subscriptionDays": 5,
"name": "Course 1",
"_id": {
"_id": "5944d5bc32c6ae2930174289",
"__v": 0,
"name": "Course 1",
"info": "blah blah blah"
},
"daysPresent": []
},
{
"subscriptionDays": 5,
"name": "Course 2",
"_id": {
"_id": "5944d5bc32c6ae293017428a",
"__v": 0,
"name": "Course 2",
"info": "fubble rumble"
},
"daysPresent": [
"2017-06-17T07:09:48.662Z"
]
}
]
},
{
"_id": "5944d5bc32c6ae293017428c",
"__v": 0,
"name": "Ted",
"email": "ted#example.com",
"courses": []
}
]

Answer 2

Schema you can define like:-
var mongoose = require('mongoose');
var courseSchema = new mongoose.Schema({
name: String
});
var studentSchema = new mongoose.Schema({
name: String,
email: { type: String, unique: true},
phone: String,
gender: String,
age: String,
city: String,
street: String,
picture: String,
courses: [{
course:{type:mongoose.Schema.Types.ObjectId,ref:'courseSchema'},
isAttending:{type:Boolean ,default:false}
}],
subscriptionDays: Number,
daysPresent: [Date]
}, schemaOptions);
module.exports = mongoose.model('Student', studentSchema);
isAttending will solve your problem if studen subscribe 3 courses and going to particular one course then isAttending will be true otherwise false.
You Can use Cron npm module which will run a function on what time will you set and its make your life easy.
Thanks