Node.js find() in Mongoose model definition

Question

I want to define a method on my model that involves searching the documents of the same model, here is what I tried:

var mongoose = require('mongoose');
var Author = require('./author.js'); 

var bookSchema = mongoose.Schema({
    author : { type: mongoose.Schema.Types.ObjectId, ref: 'author' },
    genre: String,
});

bookSchema.methods.findSimilar = function(callback) {
    bookSchema.find({'genre': this.genre}).exec(function doThings(err, doc){ 
        /* ... */ 
    }); 
}; 
module.exports = mongoose.model('book', bookSchema, 'book');

However, I get TypeError: bookSchema.find is not a function.

I also tried bookSchema.methods.find(), same result. How can I fix this?

Thanks,

Edit: Inspired by this answer, I also tried this.model('Book').find(), but I get a similar error: TypeError: this.model is not a function

Answer 1

Change your method to: (I assume you have already exported model Book from your schema module.

bookSchema.methods.findSimilar = function(callback) {

    this.model('Book').find({'genre': this.genre}).exec(function doThings(err, doc){ 
        /* ... */ 

    }); 

    // Or if Book model is exported in the same module
    // this will work too:
    // Book.find({'genre': this.genre}).exec(function doThings(err, doc){ 
    //     /* ... */ 
    //    
    // }); 
};

The method will be available on the instance of your model:

var book = new Book({ author: author_id, genre: 'some_genre' });
// Or you could use a book document retrieved from database

book.findSimilarTypes(function(err, books) {
    console.log(books);
});

See documentation here.

EDIT (Complete Schema/Model Code)

The complete schema/model code will be as follows:

var mongoose = require('mongoose');
var Author = require('./author.js'); 

var BookSchema = mongoose.Schema({
    author : { type: Schema.Types.ObjectId, ref: 'Author' },
    genre: String,
});

BookSchema.methods.findSimilar = function(callback) {
    Book.find({genre: this.genre}).exec(function doThings(err, doc){ 
        /* ... */ 
    }); 
}; 

const Book = module.exports = mongoose.model('Book', BookSchema);

Usage example:

var book = new Book({ author: author_id, genre: 'some_genre' });
// Or you could use a book document retrieved from database

book.findSimilarTypes(function(err, books) {
    console.log(books);
});

Answer 2

You forgot to write new keyword, so do this :

var bookSchema = new mongoose.Schema({
    author : { type: mongoose.Schema.Types.ObjectId, ref: 'author' },
    genre: String,
});

Cheers:)