app.js

app.js

const express = require('express');
const { ObjectId } = require('mongodb');
const  {connectToDb, getDb} = require('./db');

//Initiate app and middleware
const app = express();
app.use(express.json())

//db connection
let db;

connectToDb((err)=>{
    if(!err){
        app.listen(3000, ()=>{
            console.log("App listening on port 3000");
        })
        db = getDb()
    }
})


//Fetching all the documents in a collection
app.get('/books', (req, res)=>{
    //Pagination
    //Getting the current page
    const page = req.query.p || 0 //if nothing is passed in query params then we will assume it to be first page as 0
    const booksPerPage = 1

    let books = [];
    //Getting refrence to the Books Collection
    db.collection('Books')
    .find() //cursor toArray forEach
    .sort({author:1})
    .skip(page*booksPerPage) //skip these many docs from this collection
    .limit(booksPerPage)
    .forEach(book=> books.push(book))
    //forEach is asynchronous
    .then(()=>{
        res.status(200).json(books)
    })
    .catch(()=>{
        res.status(500).json({error:"Could not fetch the documents"})
    })
    
})

//Fetching a single document from a collection
app.get('/books/:id', (req, res)=>{
    if(ObjectId.isValid(req.params.id)){
        db.collection('Books')
        .findOne({_id:ObjectId(req.params.id)})
        .then((doc)=>{
            res.status(200).json(doc)
        })
        .catch(err=>{
            res.status(500).json({error:"Could not fetch the document"})
        })
    }
    else{
        res.status(500).json({error: "id does not exist"})
    }
})

//POST Request
app.post('/books', (req,res)=>{
    const book = req.body;
    db.collection('Books')
    .insertOne(book)
    .then(result=>{
        res.status(201).json(result)
    })
    .catch(err=>{
        res.status(500).json({err:"Could not add a new document"})
    })
})

//Delete Request
app.delete('/books/:id', (req, res)=>{
    if(ObjectId.isValid(req.params.id)){
        db.collection('Books')
        .deleteOne({_id:ObjectId(req.params.id)})
        .then((result)=>{
            res.status(200).json(result)
        })
        .catch(err=>{
            res.status(500).json({error:"Could not delete the document"})
        })
    }
    else{
        res.status(500).json({error: "id does not exist"})
    }
})

//Update Request
app.patch('/books/:id', (req, res)=>{
    if(ObjectId.isValid(req.params.id)){
        db.collection('Books')
        .updateOne({_id:ObjectId(req.params.id)}, {$set:req.body})
        .then((result)=>{
            res.status(200).json(result)
        })
        .catch(err=>{
            res.status(500).json({error:"Could not update the document"})
        })
    }
    else{
        res.status(500).json({error: "id does not exist"})
    }
})