[SOURCES]

• https://www.tutorialspoint.com/firebase
• https://firebase.google.com/docs/database/web
• https://howtofirebase.com/firebase-data-modeling-939585ade7f4

SAVING AND UPDATING DATA

https://www.tutorialspoint.com/firebase/firebase_write_data.htm SETTING var playersRef = firebase.database().ref("players/"); playersRef.set ({ John: { number: 1, age: 30 },

Amanda: { number: 2, age: 20 } });

UPDATING var johnRef = firebase.database().ref("players/John"); johnRef.update ({ "number": 10 });

PUSHING (automatically provides unique ID) var playersRef = ref.child("players"); playersRef.push ({ name: "John", number: 1, age: 30 });

GETTING KEY (basically ID, unique or not) We can get any key from Firebase by using the key() method. For example, if we want to get our collection name, we could use the following snippet.

var ref = new Firebase('https://tutorialsfirebase.firebaseio.com'); var playersRef = ref.child("players"); var playersKey = playersRef.key(); console.log(playersKey); // => "players"

TRANSACTIONAL DATA (retrieving only for updating purpose) Transactional data is used when you need to return some data from the database then make some calculation with it and store it back. We want to retrieve property, add one year of age and return it back to Firebase. The amandaRef is retrieving the age from the collection and then we can use the transaction method. We will get the current age, add one year and update the collection.

var ref = new Firebase('https://tutorialsfirebase.firebaseio.com');

var amandaAgeRef = ref.child("players").child("-KGb1Ls-gEErWbAMMnZC").child('age');

amandaAgeRef.transaction(function(currentAge) { return currentAge + 1; });

READING DATA

We can use the on() method to retrieve data. This method is taking the event type as "value" and then retrieves the snapshot of the data. When we add val() method to the snapshot, we will get the JavaScript representation of the data.

var ref = firebase.database().ref();

ref.on("value", function(snapshot) { console.log(snapshot.val()); }, function (error) { console.log("Error: " + error.code); });

• Application side joins (you can query many sources at once [kinda])

var userRef = ref.child(‘users/’ + userId);
var userTransactionsRef = ref.child(‘transactions/’ + userId);
Promise.all([
 userRef.once(‘value’),
 userTransactionsRef.once(‘value’)
]).then(function (snaps) {
 var user = snaps[0].val();
 var userTransactions = snaps[1].val();
});

READING AUTOMIZED (EVENTS)

1. value This event type will be triggered every time the data changes and it will retrieve all the data including children.

2. child_added This event type will be triggered once for every player and every time a new player is added to our data. It is useful for reading list data because we get access of the added player and all previous players. var playersRef = firebase.database().ref("players/");

playersRef.on("child_added", function(data, prevChildKey) { var newPlayer = data.val(); console.log("name: " + newPlayer.name); console.log("age: " + newPlayer.age); console.log("number: " + newPlayer.number); console.log("Previous Player: " + prevChildKey); });

Most beginning Firebase users initially prefer the value event because it’s so easy to reason about; however, more sophisticated users tend to use child_added wherever possible, because child_added places less load on the server running your Firebase, so it scales better. Also, since child_added respects sort order, you don’t have to manually sort the data on your client.

3. child_changed This event type is triggered when the data IN REFERENCE CHILD has changed. var playersRef = firebase.database().ref("players/");

playersRef.on("child_changed", function(data) { var player = data.val(); console.log("The updated player name is " + player.name); });

4. child_removed If we want to get access of deleted data, we can use child_removed event type. var playersRef = firebase.database().ref("players/");

playersRef.on("child_removed", function(data) { var deletedPlayer = data.val(); console.log(deletedPlayer.name + " has been deleted"); });

DETACHING CALLBACKS (removing events listeners from data)

1. Detach Callback for Event Type Let us say we want to detach a callback for a function with value event type.

Example var playersRef = firebase.database().ref("players/");

ref.on("value", function(data) { console.log(data.val()); }, function (error) { console.log("Error: " + error.code); }); We need to use off() method. This will remove all callbacks with value event type. playersRef.off("value");

2. Detach All Callbacks When we want to detach all callbacks, we can use:

playersRef.off();

QUERYING ORDERED DATA: var playersRef = firebase.database().ref("players/");

playersRef.orderByChild("name").on("child_added", function(data) { console.log(data.val().name); });

You can order by:

1. child field - orderByChild($fieldNameAsString)
2. key - orderByKey() (no param)
3. value - orderByValue() (no param)

Generally you can:

1. CRUD manually - like in every DB (use one of below links and choose one of the CRUD chapters from left menu on TutorialsPoint page)
2. Listen for events on data and its fields (remove events listeners as well) https://www.tutorialspoint.com/firebase/firebase_event_types.htm
3. Order data with predefined methods https://www.tutorialspoint.com/firebase/firebase_queries.htm
4. Filter data with predefined methods https://www.tutorialspoint.com/firebase/firebase_filtering_data.htm
5. Use predefined authentication methods (supported OOTB) https://www.tutorialspoint.com/firebase/firebase_email_authentication.htm

• email/pass
• google
• facebook
• github
• anonymous

6. check if connection to FB DB is alive: var connectedRef = firebase.database().ref(".info/connected");

connectedRef.on("value", function(snap) { if (snap.val() === true) { alert("connected"); } else { alert("not connected"); } });

7. Support offline OOTB
8. Do synchonous updates to many tables - in one query!

Best practices

• think about how will you query your data and structure it accordingly
• avoid nesting data
• keep your data flat
• if you choose to duplicate your data here and there remember to always update it in all places. Keeping track of it in some external documentation is probably a good idea, so you remember all relations.
• application side joins
• prefer 'child_added' event instead of 'value' event