Mongoose Query.prototype.$where() API

The Mongoose Query API.prototype.$where() method of the Mongoose API is used on the Query objects. It allows us to put the where condition in the form of JavaScript object or a function in order to pass the expression to the mongodb system. Let us understand the $where() method using an example.

Syntax:

query.$where( js );

Parameters: This method accepts a single parameter as described below:

• js: It is used to specify the JavaScript expression or function.

Return Value: This method returns query object.

Setting up Node.js Mongoose Module:

Step 1: Create a Node.js application using the following command:

npm init

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

npm install mongoose

Project Structure: The project structure will look like this: 

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Database Structure: The database structure will look like this, the following database present in the MongoDB.

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Example 1: The below example illustrates the basic functionality of the Mongoose Connection $where() method. We are fetching the document from collection where name is equal to "Student1".

Filename: app.js

Step to run the program: To run the application execute the below command from the root directory of the project:

node app.js

Output:

[
 {
 _id: new ObjectId("63c2fe2ef9e908eb17f225da"),
 name: 'Student1',
 age: 25,
 rollNumber: 36,
 __v: 0
 }
]

Example 2: The below example illustrates the basic functionality of the Mongoose Connection $where() method. We are fetching the documents from the collection where age is greater than and equal to 18.

Filename: app.js

Step to run the program: To run the application execute the below command from the root directory of the project:

node app.js

Output:

Result - [
 {
 _id: new ObjectId("63c2fe2ef9e908eb17f225da"),
 name: 'Student1',
 age: 25,
 rollNumber: 36,
 __v: 0
 },
 {
 _id: new ObjectId("63c2fe2ef9e908eb17f225db"),
 name: 'Student2',
 age: 18,
 rollNumber: 65,
 __v: 0
 }
]

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