Firebase

Question 1

What is firebase?

Answer 1

Backend as a service

Question 2

how to establish a connection to firebase database

Answer 2

import * as firebase from ‘firebase’;

const firebaseConfig = {
apiKey: “AIzaSyAdcTBkULme5gAMwksm7n4aSm9uRVXVkTQ”,
authDomain: “expensify-3a1e5.firebaseapp.com”,
databaseURL: “https://expensify-3a1e5.firebaseio.com”,
projectId: “expensify-3a1e5”,
storageBucket: “expensify-3a1e5.appspot.com”,
messagingSenderId: “932279113711”,
appId: “1:932279113711:web:d77772e36517d5065b881a”
};

firebase.initializeApp(firebaseConfig);

Question 3

How to write to the database?

Answer 3

firebase.database().ref().set({name:’Chris’});

Question 4

How to update a value in the database?

Answer 4

firebase.database(‘user’).ref(‘name’).set({name:’Chris’});

Question 5

How to remove data values from database?

Answer 5

firebase.database(‘user’).ref(‘name’).remove();

Question 6

How to update values in the database?

Answer 6

firebase.database(‘user’).ref().update({key:value});

when updating children of a property, need to use {key/child:’value’}

Question 7

How to read from the databse?

Answer 7

database.ref('propertyToAccess').once('value').then((snapshot)=>{
    const val = snapshot.val()
    console.log(val)
}).catch((error)=>{
    console.log(error)
})

Question 8

How to subsribe to a database so that it notifies you each time a change occurs

Answer 8

database.ref().on(‘value’,(snapshot)=>{
console.log(snapshot.val())
})

Question 9

How to remove a subscription to database?

Answer 9

database.ref().off((snapshot)=>{
console.log(snapshot.val())
})

Question 10

What datatype does firebase database not support?

Answer 10

Arrays

Question 11

What happens when you try and save an array in firebase database?

Answer 11

firebase turns the array into an object with array indices as keys

Question 12

what does database.ref().push() do?

Answer 12

it creates a unique id for the element and saves the element as a child of the unique id

Question 13

When saving and retrieving arrays from firebase database, which methods should be used

Answer 13

Storing and array

expenses.forEach((expense)=>{
database.ref(expenses).push(expense)
})

when retreiving, call forEach on snapshot

database.ref().once('value').then((snapshot)=>{
    const expenses = []
    snapshot.forEach((childSnapshot)=>{
        expenses.push({
            id:childSnapshot.key,
            ...childSnapshot.val()
        })
    })

}).catch((error)=>{
console.log(error)
})

Question 14

name the different subcription methods

Answer 14

val()
child_removed()
child_changed()
child_added()