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Mongoose SchemaType.prototype.transform() API

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Mongoose is a MongoDB object modeling and handling for a node.js environment. Mongoose SchemaType transform is a SchemaType method that allows us to transform or manipulate a path when converting a document into JSON. Mongoose uses the current value of the path as a parameter for the method. Let’s understand more about this with some examples.

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.

 

Example 1: In this example, we will create a transform function that will give us the year of the data stored in a path.

Filename: main.js

Javascript




const mongoose = require('mongoose')
  
// Database connection
    dbName: 'event_db',
    useNewUrlParser: true,
    useUnifiedTopology: true
}, err => err ? console.log(err) : 
    console.log('Connected to database'));
  
const personSchema = new mongoose.Schema({
    date: {
        type: Date,
        transform: v => v.getFullYear()
    }
});
  
const Person = mongoose.model('Person', personSchema);
const person = new Person({ date: new Date() });
console.log(person.toJSON().date);


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

node main.js

Output:

 

Example 2: In this example, we will create a transform function that will give us the full name of a person from an Array of first names and Last names.

Filename: main.js

Javascript




const mongoose = require('mongoose')
  
// Database connection
    dbName: 'event_db',
    useNewUrlParser: true,
    useUnifiedTopology: true
}, err => err ? console.log(err) : console.log('Connected to database'));
  
const personSchema = new mongoose.Schema({
    name: {
        type: Array,
        transform: v => v.join(' ')
    }
});
  
const Person = mongoose.model('Person', personSchema);
const person = new Person({ name: ['John', 'Doe'] });
console.log(person.toJSON().name);


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

node main.js

Output:

 

Reference: https://mongoosejs.com/docs/api/schematype.html#schematype_SchemaType-transform



Last Updated : 02 Nov, 2022
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