Can not populate array of objects

Question

EDIT added mongoose.model.

I'm pretty new to mongodb and mongoose. I'm not able to populate books to authors in mongoose. Can anyone help me with that? Here is my code. I removed unnecessary fields

const authorSchema = mongoose.Schema({
    _id:{
        type: String,
        required: true,
        unique: true,
        trim: true
    },
    name: {
        type: String,
        required: true,
        trim: true
    },
    books: [{
        type: String,
        ref: "Book"
    }]
}, {_id:false})

const Author = mongoose.model('Author', authorSchema)

module.exports = {Author}

And my books schema looks as following

const bookSchema = mongoose.Schema({
    _id:{
        type:String,
        required:true,
        unique:true,
        trim: true
    },
    name: {
        type: String,
        required: true,
        trim: true,
        unique: true
    },
    description:{
        type: String,
        trim: true,
        default: 'No description specified'
    },
    datePublished: {
        type: Date,
        trim: true,
        default: '01/01/2001'
    },
    author:{
        type: String,
        ref: 'Author',
        required: true
    }
}, {_id:false})
const Book = mongoose.model('Book', bookSchema)

module.exports = {Book}

Here is the route to populate them together

AuthorRouter.get('/authors/:id', async(req, res)=>{
    const authorID = req.params.id
    try {
        const author = await Author.findById(authorID)
        try {
            const populated = await author.populate({path: 'books.book', select: 'name description -_id'})
            console.log(populated);
            res.status(201).send(populated)
        } catch (e) {
            res.status(401).send(`${e}\n Unable to populate categories`)
        }
        
    } catch (error) {
        res.status(401).send('Unable to find author')
    }
})

Output is following with empty books array:

{
    "_id": "123",
    "name": "testuser",
    "books": [],
    "__v": 0
}

Where in the code did you specify the Mongoose.model function? — Tyler2P
– Tyler2P, Commented Dec 29, 2021 at 18:59
@Tyler2P at the end of the Schemas. I've just added them to code — IT ACADEMY
– IT ACADEMY, Commented Dec 29, 2021 at 19:02

eol · Accepted Answer · 2021-12-29 19:20:10Z

2

Populating an arrays of refs works the same way as a single ref. Just call the populate method on the query and an array of documents will be returned in place of the original _id's.

In your case that would be:

const populated = await author.populate({path: 'books', select: 'name description -_id'});

answered Dec 29, 2021 at 19:20

eol

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Comments

Diwas Acharya · Accepted Answer · 2021-12-30 08:42:00Z

Hey i have modify your code , try to use this one

This is your author schema file

const Schema = mongoose.Schema;
const authorSchema = mongoose.Schema({
    _id:{
        type: String,
        required: true,
        unique: true,
        trim: true
    },
    name: {
        type: String,
        required: true,
        trim: true
    },
    books: [{
        type: Schema.Types.ObjectId,
        ref: "bookSchema"
    }]
}, {_id:false})

const Author = mongoose.model('Author', authorSchema)

module.exports = {Author}

And this is your route


AuthorRouter.get('/authors/:id', async(req, res)=>{
    const authorID = req.params.id
    try {
        const author = await Author.findById(authorID)
        try {
            const populated = await author.find().populate('books');
            console.log(populated);
            res.status(201).send(populated)
        } catch (e) {
            res.status(401).send(`${e}\n Unable to populate categories`)
        }
        
    } catch (error) {
        res.status(401).send('Unable to find author')
    }
})

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