CODEWITHSUNDEEP
node.jsmongoose
Adnan Babai
Adnan Babai

Reputation: 65

How to use findById() for nested array's in mongoose?

Error Image Actually i've an Object in which i have an array of semesters, each semester has an array of subjects and each subject has an array of lessons. I want to add lesson to its respective semester and subject. I use findById to find respective semester from Object but when i use findById again to find particular subject from array of subj's. It gives me error.

Semester.findById(req.body.semesterId).populate({ path: 'subjects' })
        .exec((err, model) => {

           [model.subjects.findById(req.body.subjectId, (err, model) => {
                console.log(model)
            })][1]
        })
})

Upvotes: 0

Views: 577

Answers (1)

dillon
dillon

Reputation: 733

I would personally structure my Schema's like so:

const semesterSchema = mongoose.Schema({
    number: { type: Number, required: true },
    subjects: [{ type: mongoose.SchemaTypes.ObjectId, ref: 'Subject' }]
})

const subjectSchema = mongoose.Schema({
    semester: { type: mongoose.SchemaTypes.ObjectId, ref: 'Semester', required: true },
    title: { type: String },
    lessons: [{ type: mongoose.SchemaTypes.ObjectId, ref: 'Lesson' }]
})

const lessonSchema = mongoose.Schema({
    semester: { type: mongoose.SchemaTypes.ObjectId, ref: 'Semester', required: true },
    subject: { type: mongoose.SchemaTypes.ObjectId, ref: 'Subject', required: true },
    title: { type: String },
    test: { type: Object }
})

What this does is provides cyclical references to my schemas which is quite nice in some cases.

To solve the case your describing, we could do something like this:

const { semesterId, subjectId } = req.body; // destructure variables needed from body

Semester
    .findById(semesterId)
    .populate({ path: 'subjects' })
    .lean() // use lean() if you only require the document and not the entire mongoose object. i.e. you do not require .save(), .update(), etc methods.
    .exec((err, semester) => {
        const subject = semester.subjects.find(subject => subject._id === subjectId );
        console.log(subject);
    });

// ****** THIS ASSUMES YOU HAVE FOLLOWED MY DEFINED SCHEMA ABOVE ********

Alternatively, you could directly query the subject and populate the semester if you want that data like so:

const { semesterId, subjectId } = req.body;

Subject
    .findById(subjectId)
    .populate({ path: 'semester' })
    .lean()
    .exec((err, subject) => {
        console.log(subject);
    });

// ****** THIS ASSUMES YOU HAVE FOLLOWED MY DEFINED SCHEMA ABOVE ********

Upvotes: 1

Related Questions