Mongoose Query prototype.where() API

Mongoose is a MongoDB object modeling and handling for a node.js environment. Mongoose Query where() method is used to filter the documents from a collection using the MongoDB query system. It can be used in various ways, like chaining or passing query conditions. Let’s understand more about this with some examples.

Syntax:

Query.prototype.where()

Parameters: It accepts 2 parameters that are described below:: 

• path: It is of type String or Object.
• val: It can be of any type.

Return type: It returns the Query object.

Creating node application And Installing Mongoose:

Step 1: Create a node application using the following command:

mkdir folder_name
cd folder_name
npm init -y
touch main.js

Step 2: After creating the ReactJS application, Install the required module using the following command:

npm install mongoose

Project Structure: It will look like the following.

GUI Representation of the  Database using MongoDB Compass: Currently, the collection has no data.

Example 1: In this example, we will use Query where() method to filter out the documents using the chaining method where we would chain different queries together.

Filename: main.js

Javascript

const mongoose = require('mongoose')

// Database connection
mongoose.connect('mongodb://localhost:27017/query-helpers', {
    dbName: 'event_db',
    useNewUrlParser: true,
    useUnifiedTopology: true
}, err => err ? console.log(err) :
    console.log('Connected to database'));

const personSchema = new mongoose.Schema({
    name: {
        type: String,
    },
    age: {
        type: Number,
    }
});

const personsArray = [
    {
        name: 'John',
        age: 22
    },
    {
        name: 'Dave',
        age: 17
    },
    {
        name: 'Earl',
        age: 12
    }
]

const Person = mongoose.model('Person', personSchema);

(async () => {
    await Person.insertMany(personsArray);
    const persons =
        await Person.find().where('age').gte(18);
    console.log(persons);
})()

Step to Run Application: Run the application using the following command from the root directory of the project:

node main.js

Output: We see that the value remains unchanged in the result.

GUI Representation of the  Database using MongoDB Compass:

Example 2: In this example, we will use Query API where() method to filter out the documents by passing query conditions as the argument to the where() method.

Filename: main.js

Javascript

const mongoose = require('mongoose')

// Database connection
mongoose.connect('mongodb://localhost:27017/query-helpers', {
    dbName: 'event_db',
    useNewUrlParser: true,
    useUnifiedTopology: true
}, err => err ? console.log(err) :
    console.log('Connected to database'));

const personSchema = new mongoose.Schema({
    name: {
        type: String,
    },
    age: {
        type: Number,
    }
});

const personsArray = [
    {
        name: 'John',
        age: 22
    },
    {
        name: 'Dave',
        age: 17
    },
    {
        name: 'Earl',
        age: 12
    }
]

const Person = mongoose.model('Person', personSchema);

(async () => {
    await Person.insertMany(personsArray);
    const persons = await Person.find().where
        ({ age: { $lte: 18 } })
    console.log(persons);
})()

Step to Run Application: Run the application using the following command from the root directory of the project:

node main.js

Output: We see that the value remains unchanged in the result.

GUI Representation of the  Database using MongoDB Compass:

Reference: https://mongoosejs.com/docs/api/query.html#query_Query-where