CRUD operations using Mongoose in NodeJS

Connection to MongoDB

To establish a connection to MongoDB first we need to import mongoose module to our project which is available in the NPM registry.

const mongoose = require('mongoose');

mongoose.connect('mongodb://localhost/play')
    .then(() => console.log('Connected to database'))
    .catch(err => console.log('could not connect to the mongo db'));

** Schema **

Once the connection established we need to define a schema. We use schema to define the shape of a document within a collection in MongoDB. Schema is specific to the mongoose.

Let's see how to design a schema

const courseObj = new mongoose.Schema({
    name: {
        type:String, 
        required: true,
        minlength: 5,
        maxlength: 255
    },
    category:{
        type: String,
        enum: ['web', 'db', 'Mobile', 'Network']
    },
    author: String,
    tags: {
        type: Array
    },
    date: {type: Date, default: Date.now},
    isPublished: Boolean,
})

List of types in Schema

String, Number, Date, Buffer, Boolean, ObjectId, Array

** Model**

Once we create a schema we need to compile that schema into a model. Schema is a class and model is an object to the class.
Let's create a model for the above schema.

const Course = mongoose.model('Course', courseObj);

//mongoose.model method takes two parameters first argument is for collection to which this model is for and another is schemaObject.

** CRUD Operations **

** Create **

Once we create a model then we can create, read, update and delete a document from the database. Let's see how to create a document in the database.

async function createCourseObj(){
    const course = new Course({
        name: 'Java course',
        category: 'db',
        author: 'Madhav',
        // tags: ['Java', 'Backend'],
        isPublished: true,
        price: 15
    })
    try {
        const result = await course.save(); //save method is used to store a document
        console.log('result',result);

    }
    catch(err) {
        console.log(err)
        
    }
    
}

** Read **:

Let's see how to query a document

async function getCourses(){
    const courses = await Course
    //.find({price: {$gte: 10}})
    .find()
    .or([{author: 'madhav'}, {isPublished:true}])
    .limit(5)
    .select({name: 1, tags: 1});
    console.log(courses);
//find method is used to query a document
}

** Update **:

To update a document

async function updateCourse(id) {
    const course = await Course.findByIdAndUpdate(id,  {
        $set: {
            author: 'Krishna',
            isPublished: true
        }
    }, {new: true});
    console.log(course);
    
}

** Delete **:

To remove a document from the database

async function deleteCourse(id) {
    const course = await Course.findByIdAndRemove({_id: id});
    console.log(course);
}