Error: addReview is not a function in MERN application - node.js

Question

I'm following along with a tutorial to create a movie review app on the MERN stack.
When calling my API using Insomnia, I'm getting the error "ReviewsDAO.addReview is not a function"
reviewsDAO.js:
import mongodb from "mongodb"
const ObjectId = mongodb.ObjectId
let reviews
export default class ReviewsDAO{
static async injectDB(conn){
if(reviews){
return
}
try { reviews = await conn.db(process.env.MOVIEREVIEWS_NS).collection('reviews')}
catch(e){
console.error(`unable to establish connection handle in reviewDAO: ${e}`)
}
}
static async addReview(movieId, user, review, date){
try{
const reviewDoc = {
name: user.name,
user_id: user._id,
date: date,
review: review,
movie_id: ObjectId(movieId)
}
return await reviews.insertOne(reviewDoc)
}
catch(e) {
console.error(`unable to post review ${e}`)
return {error: e}
}
}
reviews.controller.js:
import ReviewsDAO from '../dao/reviewsDAO.js'
export default class ReviewsController{
static async apiPostReview(req,res,next) {
const reviewsDAO = new ReviewsDAO()
try{
const movieId = req.body.movie_id
const review = req.body.review
const userInfo = {
name: req.body.name,
_id: req.body.user_id
}
const date = new Date()
const ReviewResponse = await reviewsDAO.addReview(
movieId,
userInfo,
review,
date
)
res.json({status: "success"})
}
catch(e) {
res.status(500).json({error: e.message})
}
}
The reviews collection is also not being created in MongoDB. But maybe that isn't supposed to happen until we create our first review.
Why isn't my function being called appropriately?

Answer 1

You need to instantiate a ReviewsDAO object in order to call its methods.
const reviewsDAO = new ReviewsDAO()
Then you will be able to access the addReview() method

Answer 2

You are calling the class method without initializing the object.
For example:
class Animal{
function sayhello(){
console.log("Hello")
}
}
// I can call the sayhello method by creating an object.
var dog=new Animal()
dog.sayhello() //prints "Hello"
But in your case, you are calling the method without creating the object.
Animal.sayhello()
// It will create an error
So initialise the object and call the method
const reviewsDAO = new ReviewsDAO()
reviewDAO.addreviews()
The static keyword defines static methods for classes.
Static methods are called directly on the class (Car from the example above) - without creating an instance/object (mycar) of the class
So
const Reviewsdao= new ReviewsDAO()
ReviewsDAO().addreviews()
Call the method with the class name after initialising it.