{ JavaScript } MongoDB - Jaydon Learning Blog

MongoDB

What is MongoDB?

MongoDB is an open-source database program that organizes data by using documents.
- Uses JSON-like documents with optional schemas.
- Uses key-value pairing to associate data objects with properties.
MongoDB Atlas is the global cloud database on AWS, Azure, and GCP
MongoDB also has an ORM that is called Mongoose.

NoSQL Databases (SQL VS NOSQL)

SQL - Structured data schema(Strict) & data is set to several tables linked with a ‘relationship’
NoSQL - No Schema, No relationship, and JSON-like data format

Commands

use {dbname}: Create db (if it doesn’t exist) & switch to a specific db → Note that you won’t see your new database in the list of databases until data is added.
Specify a collection name = data model: storing all documents related to that model within the same group.

e.g. within recipe app(db) , there is a group (collection) named as ‘contacts’, and its data (documents)

Insert:
- db.inventory.insertOne
- db.inventory.insertMany
Find:
- find({key:”value”}) - findOne - findMany db.contacts.find({id: ObjectId(“6241cb3b6d1c4b70d50a75b1”)}) db.contacts.find({name:”Jon”})
Delete
- db.collection.deleteMany()
- db.collection.deleteOne()
Update
- What is the use of ‘set’ in MongoDB?
  - In MongoDB, the $set operator is used to replace the value of a field to the specified value.

Syntax: , { $set: { <field1>: <value1>, ... } }
db.contacts.update({name:"jon wexler"}, {$set:{email:”jonjwexler@gmail.com”}})

select a db: use choose_db
show all dbs: show dbs
show collections in a db: use choose_db then show collections
show all records in a db: use choose_db then db.users.find()
delete a db: use choose_db then db.dropDatabase()
to see which db is being used: db

Setting up Mongoose with your Node.js application

Index.js (main.js)

const express = require("express");
const mongoose = require("mongoose");
const app = express();
const port = 3000;

/**
 * Connect to our Mongo DB
 * We are returned a promise; then & catch
 * tells what to do when it succeeds .(then) and
 * what to do when it fails (.catch)
 */
mongoose
  .connect("mongodb://localhost:27017/usersDB2", {
    useNewUrlParser: true,
  })
  .then((data) => {
    console.log("Mongo DB connection success!");
  })
  .catch((err) => {
    console.log("Mongo DB connection failed: " + err.message);
  });

// Create a schema
const userSchema = new mongoose.Schema({
  name: String,
  email: String,
  fav_pizza: String,
  personalities: [String],
});

// Apply it to a model
const User = mongoose.model("User", userSchema);
// User has to be with capital first letter. mongo will make that small and pluralize
// the model name: "User" => "users"

// Creating

const pj = new User({
  name: "PJ",
  email: "BIGID@gmail.com",
  fav_pizza: "Pepperoni",
  personalities: ["Challenging","Kind"],
});

const hj = new User({
  name: "Hyukjoo Lee",
  email: "lee@gmail.com",
  fav_pizza: "Pepperoni",
  personalities: ["Dedicated", "Detailed"],
});

User.insertMany([pj, hj, cr], function (err) {
  if (err) {
    console.log(err);
  } else {
    console.log("Successfully created db");
  }
});

// Create a simple path for the home page
// Will take the usual request, response,
// and next arguments needed for this sort of function

app.use("/", (req, res, next) => {
  res.json({
    confirmation: "success",
    data: "This is the mongo project!",
  });
});

app.listen(() => {
  console.log("app is listening " + port);
});

Creating a schema

As mentioned, MongoDB itself is a schema-less database. However, Mongoose enforces schemas on our behalf to help maintain data integrity.
Note that MongoDB has ORM (Object Relational Mapping)

Read.js

const mongoose = require("mongoose");

//create and/or connect to a db
mongoose.connect("mongodb://localhost:27017/usersDB2", {
  useNewUrlParser: true,
});

// Create a schema
const userSchema = new mongoose.Schema({
  name: String,
  email: String,
  fav_pizza: String,
  personalities: [String],
});

// Apply it to a model
const User = mongoose.model("User", userSchema);
// User has to be with capital first letter. mongo will make that small and pluralize
// the model name: "User" => "users"

// Read All Data
User.find(function (err, users) {
  if (err) {
    console.log(err);
  } else {
    // console.log(users);
    // if we want to show only the names the following code does
    users.forEach(function (user) {
      console.log(user);
      // closing the connection: good practice
      mongoose.connection.close();
    });
  }
});

Update.js

User.updateOne(
  { _id: "624210c0601f212f1c76367e" },
  { name: "updated" },
  function (err) {
    if (err) {
      console.log(err);
    } else {
      console.log("marking");
    }
  }
);

Delete.js

User.deleteOne({ _id: "624210c0601f212f1c76367e" }, function (err) {
  if (err) {
    console.log(err);
  } else {
    console.log("deleted");
  }
});