MongoDB

Question 1

What kind of database is mongoDB?

Answer 1

NoSQL

Question 2

What is NoSQL

Answer 2

Not only stuctured query langauge

Question 3

Difference between SQL and noSQL?

Answer 3

SQL stores data in a table. An entry is called a row/record. Individual items in a row are called a column

noSQL stores data in a collection (looks like JSON). An entry is called a document. Individual items in a document are called fields

Question 4

Installing community edition on machine

Answer 4

Download
Rename folder and move to User directory
Create another folder with same name + -data
in terminal run: mongod.exe –dbpath=/Users/DRPC/mongodb-data

Question 5

How to start database?

Answer 5

In the terminal from the mongodb folder run:

mongod.exe –dbpath=/Users/DRPC/mongodb-data

Question 6

What is robo3t?

Answer 6

a GUI tool for working with mongodb

Question 7

What language does the mongo shell use?

Answer 7

javascript

Question 8

How to check if connection to data base was successful using the mongo shell?

Answer 8

run in console:

db.version()

Question 9

What do we need to install in order to interact with a mongoDB database from node?

Answer 9

mongoDb driver

npm i mongodb

Question 10

How to connect to mongoDB using node?

Answer 10

const mongodb = require(‘mongodb’);

const MongoClient = mongodb.MongoClient;

const connectionURL = 'mongodb://127.0.0.1:27017';
const databaseName = 'task-manager';

MongoClient.connect(connectionURL,{useNewUrlParser:true,useUnifiedTopology: true },(error,client)=>{
if(error){
return console.log(‘Unable to connect to database’)
}

const db = client.db(databaseName)

});

Question 11

What is the structure of a mongoDB database?

Answer 11

MongoDB contains databases

Databases contain collections

Collections contain documents

Documents contain fields

Question 12

how to insert a document into a collection?

Answer 12

db.collection(‘users’).insertOne({
name:’Andrew’,
age:27
},(error,result)=>{
if(error){
return console.log(‘Unable to insert user’)
}

    console.log(result.ops)
})

Question 13

How to create a MongoDb client?

Answer 13

const mongodb = require(‘mongodb’)

const MongoClient = mongodb.MongoClient

MongoClient(url,options,callback)

Question 14

How to create a database?

Answer 14

const db = client.db(‘database-name’)

Question 15

How to access or creat a collection within a database?

Answer 15

db.collection(‘collection-name’)

Question 16

What methods can be used to insert documents into a collection

Answer 16

.insertOne(document,callback)

.insertMany(ArrayOfDocuments,callback)

Question 17

What are gu id’s

Answer 17

globally unique identifiers. Allows mongo db to scale and handle a lot of traffic, without conflict.

Question 18

What is an Object id?

Answer 18

It is a globally unique 12 byte identifier for a document.

Each 12 byte id constist out of a 4 byte time stamp, a 5 byte random value, and a 3 byte counter starting with a random number.

Question 19

Are object id’s strings?

Answer 19

No they are 12 byte binary data

Question 20

What methods can be used to retrieve documents from a collection?

Answer 20

.find()

.findOne()

Question 21

When searching a data base for an object with a specific id, what method needs to be called an the id string?

Answer 21

new ObjectID()

Question 22

What is an important difference between the findOne and the find method?

Answer 22

The findOne method takes a callback that returns the required data.

The find method has no callback and doesn’t return anya actual data, instead it returns a cursor.

in order to get the data from the cursor, one needs to call the toArray() method and pass in a callback function.

Question 23

What is the advantage of having the find method return a cursor instead of the actual data?

Answer 23

It is much more memory efficient, especially when you don’t need the actual data, like when you only want a count of all the different entries that meet a specific criteria.

Question 24

How to retrieve multiple documents from a collection?

Answer 24

db.collection(‘users’).find({age:33}).toArray((error,response)=>{
if(error){
return console.log(‘error’)
}

    console.log(response)
})

Question 25

How to retrieve a single document from a collection

Answer 25

db.collection(‘users’).findOne({name:’Jo’},(error,user)=>{
if(error){
return console.log(error)
}

    console.log(user)
})

Question 26

What does CRUD stand for

Answer 26

Create
Read
Update
Delete

Question 27

How to write a promise?

Answer 27

const doWork = new Promise((resolve,reject)=>{
    const a = 1;
    if(a === 1){
        setTimeout(()=>{
            resolve([3,4,5])
        },5000)
    }else{
        setTimeout(()=>{
            reject("Oops")
        },5000)
    }

});

doWork.then((result)=>{
    console.log(result)
}).catch((error)=>{
    console.log(error)
});

Question 28

Name the update opperators

Answer 28

$set : sets the value of a field

$currentDate : sets the value to current date

$inc : INcrements the value of the filed by the specified amount.

$min: Only updates the field if the specified value is less than the existing field value

$max: Only updates the field if the specified value is greater than the exisitng field value

$mul : multiplies the value of the field by the specified amount

$rename : renames a field

$setOnInsert : Sets the value of a field if an update results in an insert of a document.

$unset : removes the specified field from a document

Question 29

how to update a single value in a document

Answer 29

db.collection('users').updateOne({
        _id: new ObjectID('5e901baa1161fe3bf83f7649')
    },{
        $set:{
            name:'JoJo'
        }
    }).then((result)=>{
        console.log(result)
    }).catch((error)=>{
        console.log(error)
    });

Question 30

What are the two main methods for updating a document

Answer 30

.updateOne()

.updateMany()

Question 31

how to update multiple values in a document

Answer 31

db.collection(‘users’).updateMany({
age:33
},{
$set:{
age:100
}
}).then((result)=>{
console.log(result)
}).catch((error)=>{
console.log(error)
});

Question 32

two main methods for deleting a document

Answer 32

.deleteOne()

.deleteMany()

Question 33

how to delete a single document?

Answer 33

db.collection(‘users’).deleteOne({
age:100
}).then((result)=>{
console.log(result)
}).catch((error)=>{
console.log(error)
});

Question 34

What is mongoDB Atlas?

Answer 34

Database as a service (DAAS)

Stores data on cloud

Handles replication: maintain redundant copies of data to increase data availability

Question 35

What is a cluster?

Answer 35

group of servers that store data

Question 36

What is a replica set?

Answer 36

A cluster where each server stores the same data. This means that each time a document is inserted, redundent copies are stored on each set. This means that if you lose access to a server in a cluster, you wont lose your data.

Question 37

How to retrieve a range of values?

Answer 37

gte = greater than and equal to
lt = less than

{“birth year”:{“$gte”:1985,”$lt”:1990}

Question 38

connecting to atlas from the mongo shell?

Answer 38

mongo + connection string

mongo “mongodb+srv://sandbox-xa6rd.mongodb.net/test” –username m001-student

Question 39

How to load data from the mongo shell?

Answer 39

While server is connected:

load(“filename.js”)

Question 40

How to see a list of databases in mongo shell?

Answer 40

show dbs

Question 41

How to switch to a specific database in mongo shell?

Answer 41

use db-name

Question 42

How to see a list of collection in a database from mongo shell?

Answer 42

show collections

Question 43

How to get a read out of the data in a collection from mongo shell?

Answer 43

db.databaseName.find().pretty()

Question 44

How to use mongo compass to connect to atlas?

Answer 44

click on cluster. Then click on the primary server. copy the hostname and fill out the individual fields in compass

Question 45

What is mongoose?

Answer 45

Mongoose is an Object Data Modeling (ODM) library for MongoDB and Node. js. It manages relationships between data, provides schema validation, and is used to translate between objects in code and the representation of those objects in MongoDB

Question 46

Mongoose: Creating a client

Answer 46

mongoose.connect(connectionURL,{useNewUrlParser: true,useCreateIndex:true });

Question 47

Mongoose: Creating a model

Answer 47

const User = mongoose.model('User', {
    name:{
        type:String
    },
    age:{
        type:Number
    }
});

Question 48

Mongoose: Inserting a document

Answer 48

const user = new User({
    name:"Bob",
    age:100
});

user.save().then((result)=>{
console.log(result)
}).catch((error)=>{
console.log(error)
});

Question 49

Mongoose: How to create a collection

Answer 49

A model is automatically created when a new model is defined. It takes the model name, pluralizes it and sets that as the collection name

Question 50

Mongoose: difference between data validation and sanitation?

Answer 50

validation: Specifies rules for valid data
sanitation: cleans up data, by removing unwanted characters etc

Question 51

Mongoose: How to make a field required?

Answer 51

required: true

Question 52

Mongoose: how to validate input?

Answer 52

validate(value){
      if(value < 21){
           throw new Error("Not old enough")
      }
}

Question 53

Which npm package can we use for validation?

Answer 53

npm validator

Question 54

Mongoose: String sanitation

Answer 54

lowercase: boolean, whether to always call .toLowerCase() on the value
uppercase: boolean, whether to always call .toUpperCase() on the value
trim: boolean, whether to always call .trim() on the value
match: RegExp, creates a validator that checks if the value matches the given regular expression
enum: Array, creates a validator that checks if the value is in the given array.
minlength: Number, creates a validator that checks if the value length is not less than the given number
maxlength: Number, creates a validator that checks if the value length is not greater than the given number

Question 55

Mongoose: number sanitation

Answer 55

min: Number, creates a validator that checks if the value is greater than or equal to the given minimum.
max: Number, creates a validator that checks if the value is less than or equal to the given maximum.
enum: Array, creates a validator that checks if the value is strictly equal to one of the values in the given array.

Question 56

Mongoose: How to set default on models?

Answer 56

default: “SomeDefaultValue”

Question 57

What should be done before data is entered into a database?

Answer 57

The data should be validated and sanitized.

Question 58

Mongoose: When defining the model, how can we check wether a value includes a specific expression?

Answer 58

validate(value){
    if(value.includes("phrase"){
        //do something
    }
}