Accessing Mongo database in Node app

MongoDB is no-sql non-relational database. Means data is stored as documents similar to objects in javascript.

Installation of MongoDB in Mac

• $ brew install mongodb-community
• $ brew services start mongoDb
• local install in /usr/local/var/mongodb, /usr/local/etc/ for config. ip=127.0.0.1

Commands to see database and collections

• start shell $ mongo, db shows test database, use dbname,
• db, use, show databases, show collections.
• collections is same like tables.

Operations on local database

• create datadb.createCollection('cars') or other way db.dogs.insert({ name: "Roger" })
• db.dogs.find()
• filter and retrieve entry $ db.dogs.find({name: 'Roger'}):
• findOne(),
• update datadb.dogs.remove({}) removes all entries.
• db.dogs.update({key: 'old obj'}, {key: 'new obj'})
• remove datadb.dogs.remove({name: 'sakira'})

Remote mongo database setup using Atlas

Atlas is remote database as a service.managed, hosted.

• Create account, create db user, use ip, 0.0.0.0/0 connect from everywhere , get db connected, authId.
• Create Model, first schema, is shape of document.
• .env for url, to use invironment var we need .env file with variable='string', we install dotenv, require ('dotenv').config()
• npm install mongodb, mongoose, dotenv, express. require them in .json.package.also, nodemon,
• mongoose.connect(url, {topology})
• const personSchema = new mongoose.Schema({}
• Person = mongoose.model('Person',personSchema);

we created schema personSchema and we created model Person

• We can instantiate Model Person
  then call save() with callback err,data parameters inside handler function, we call callback done(null, data). we call done, it inside again. That's it.

• we use Model.create() for many, use instance,Model.save() for single person. awe, difference.

• Model.Method takes first parameter obj, second calback.So, two callbacks, one for handler fn, and other from Model.method()
  some methods save,create,find,findOne,findById,findOneAndUpdate,findByIdAndRemove, callbacks done,done(null, data),function(err, data) {} etc to list in MongoDB & Mongoose package.

  • Model.Method takes first parameter obj, second calback.So, two callbacks, one for handler fn, and other from Model.method() // some methods save,create,find,findOne,findById,findOneAndUpdate,findByIdAndRemove, callbacks done,done(null, data),function(err, data) {} etc to list in MongoDB & Mongoose package.

Using MongoDB from Node.js

• To interface to a MongoDB database from a Node.js app
• init -y, npm install mongodb
• const mongo = require('mongodb').MongoClient

try {
  const client = await mongo.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  });
} catch (err) {
  console.error(err);
}

• Now you can select a database using the client.db() method:
• select a database const db = client.db('kennel')
• can get a collection const collection = db.collection('dogs')
• one const result = await collection.insertOne({name: 'Roger'})
• many const result = await collection.insertMany([{name: 'Togo'}, {name: 'Syd'}])
• find const items = await collection.find().toArray()

We need a handle either as a function or const variable collection,
or db.collectionName. then we add dot method.

Rest API uses routes HTTP GET / and HTTP POST /

• In Express we create server, web server
• app.get('/', (req, res) ) to send to client ,get data from database or from script.
• single data as app.get('/:id', (req, res) ) handled in script using filter(cb) from req.params. and send back using res.status(code).json()
• app.post('/', (req, res) ) to insert data to db.
• we use mongodb or postgre sql database to store local or remote.