MongoDB

• What is MongoDB

• Basic Commands

• Insert Commands

• Query Commands

• Update Commands

• Delete Commands

• `Connecting MongoDB on Atlas with mongoose`_

• Storing hashed passwords in database

What is MongoDB

• NoSQL, Non Relational database

• Store JSON

• Easy to get started

• Free cloud hosting - Atlas

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Basic Commands

show dbs
use DATABASE_NAME
show collections
db.dropDatabase()
db.COLLECTION.drop()

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Insert Commands

db.COLLECTION.insertOne({ key : "value", key : "value"}) # auto create collection
db.COLLECTION.find() # list all items in collection
db.COLLECTION.insertMany([{ key1 : "value1"}, { key2 : "value2" }])

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Query Commands

db.COLLECTION.find().limit(NUMBER)
db.COLLECTION.find().sort({ key1 : 1, key2 : -1 }) # 1 for alphabetical, -1 for reverse
db.COLLECTION.find().skip(NUMBER) # skip the first NUMBER results found
db.COLLECTION.find({ key : "value" })
db.COLLECTION.find({ key : "value" }, { key1 : 1, _id : 0})  # return field of key1 but
                                                             # not _id of the result
db.COLLECTION.find({ key : "value" }, { key1 : 0 }) # return all fields expect key1

• complex queries

  // pass an object into fields
  db.COLLECTION.find({ key : { $eq : "value" }}) # return results equal to "value"
  db.COLLECTION.find({ key : { $ne : "value" }}) # return results not-equal to "value"
  db.COLLECTION.find({ key : { $gt : "value" }}) # return results greater than "value"
  db.COLLECTION.find({ key : { $gte : "value" }}) # return results greater-than-or-eq "value"
  db.COLLECTION.find({ key : { $lt : "value" }})
  db.COLLECTION.find({ key : { $lte : "value" }})
  db.COLLECTION.find({ key : { $in : ["value1", "value2"] }}) # return results equal to
                                                            # value1 or value2
  db.COLLECTION.find({ key : { $nin : ["value1", "value2"] }}) # return results not-equal to
                                                             # value1 or value2
  # will also return if { key:null }, only checks key exists, not value
  db.COLLECTION.find({ key : { $exists : true }}) # return results that have key
  db.COLLECTION.find({ key : { $exists : false }}) # return results that don't have key
  
  ## AND query
  db.COLLECTION.find({ key : { $gt : "value" , $lt : "value" }})
  db.COLLECTION.find({ $and : [{ key1 : "value1" }, { key2 : "value2" }] }) # rarely used
  
  ## OR query
  db.COLLECTION.find({ $or : [{ key1 : { $gt : "value"} }, { key2 : "value2" }] })
  
  ## NOT query
  db.COLLECTION.find({ key : { $not : { $gt : "value" } } })  # return results not gt value
  
  ## comparing
  db.COLLECTION.find({ $expr : { $gt : ["$key1", "$key2"] } })  # return results if value of
                                                              # key1 is gt key2, $ syntax
  
  ## querying with nested keys
  db.COLLECTION.find({ "key1.NESTED_key" : "value" })
  db.COLLECTION.findOne({ key : "value" }) # return first result
  
  ## counting
  db.COLLECTION.countDocuments({ key : "value" }) # return NUMBER
  

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Update Commands

db.COLLECTION.updateOne({ key : value}, { $set : { newKey:"newValue" } }) # use $ syntax
# usually update based on "_id"
db.COLLECTION.updateOne({ _id : value}, { $inc : { key : 3 } }) # increment value of key
db.COLLECTION.updateOne({ _id : value}, { $rename : { key : "newValue" } }) # rename key
db.COLLECTION.updateOne({ _id : value}, { $unset : { key : "" } }) # remove key from object
db.COLLECTION.updateOne({ _id : value}, { $set : { key : "" } }) ## add key to object
db.COLLECTION.updateOne({ _id : value}, { $push : { key : "value" } }) # push value as array
db.COLLECTION.updateOne({ _id : value}, { $pull : { key : "value" } }) # remove from array
db.COLLECTION.updateMany({ key: { $exists : true } }, { $unset : { key :"" } }) # remove from
                                                                                # all if exist
db.books.replaceOne({ key : "value" }, { newKey : "newValue"} ) # replace all properties

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Delete Commands

db.COLLECTION.deleteOne({ key : "value" })
db.COLLECTION.deleteMany({ key : "value" })

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### Connecting MongoDB on Atlas with mongoose

````js // in connect.js (file for setting up MongoDB) const mongoose = require(‘mongoose’) const connectDB = (url) => { mongoose.connect(url) } module.exports = connectDB

// in .env file to store mongo_connection_string, gitignore this file MONGO_URI=mongo_connection_string

// in app.js require(‘dotenv’).config()

// use async as mongoose.connect() returns a promise const start = async () => {

try{

await connectDB(process.env.MONGO_URI) app.listen(PORT)

} catch (err) {

console.log(error)

}

}

• setting up schema for Atlas document

  • an instance of the model is called document

  • document by default has no schema

  ````js // schema.js in models (by convention) folder const mongoose = require(‘mongoose’) const Schema = new mongoose.Schema({ name: String, completed: Boolean })

• querying to db

  ````js const COLLECTION = require(‘../modles/collection’)

  // can directly pass as req.query is an object const findItem = await COLLECTION.find(req.query) ````

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Storing hashed passwords in database

````js // using bcryptjs const bcrypt = require(‘bcryptjs’)

const salt = await bcrypt.genSalt(10) const hashedPassword = await bcrypt.hash(password, salt) ````

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