„JavaScript + Firestore“ mokymo programa 2020 m .: mokykitės pavyzdžiu

„Cloud Firestore“ yra greita, be serverių „NoSQL“ duomenų bazė, puikiai tinkanti bet kokio dydžio žiniatinklio ir mobiliųjų programų valdymui. Paimkite išsamų „Firestore“ mokymosi vadovą, sukurtą tam, kad parodytumėte, kaip naudoti „Firestore“ kaip variklį savo nuostabiems projektams iš priekio į galą.

Turinys

Darbo su „Firestore“ pradžia

  • Kas yra „Firestore“? Kodėl turėtumėte jį naudoti?
  • „Firestore“ nustatymas „JavaScript“ projekte
  • „Firestore“ dokumentai ir kolekcijos
  • Mūsų duomenų bazės valdymas naudojant „Firebase Console“

Gaunami duomenys naudojant „Firestore“

  • Duomenų gavimas iš kolekcijos naudojant .get ()
  • Prenumeruojama kolekcija naudojant .onSnapshot ()
  • Skirtumas tarp .get () ir .onSnapshot ()
  • Kolekcijos atsisakymas
  • Atskirų dokumentų gavimas

Duomenų keitimas naudojant „Firestore“

  • Pridedamas dokumentas prie kolekcijos su .add ()
  • Dokumento pridėjimas prie kolekcijos su .set ()
  • Esamų duomenų atnaujinimas
  • Ištrinami duomenys

Esminiai modeliai

  • Darbas su subkolekcijomis
  • Naudingi „Firestore“ laukų metodai
  • Užklausa naudojant .where ()
  • Duomenų užsakymas ir ribojimas

Pastaba: galite atsisiųsti šios mokymo programos PDF versiją, kad galėtumėte ją perskaityti neprisijungę.

Kas yra „Firestore“? Kodėl turėtumėte jį naudoti?

„Firestore“ yra labai lanksti, lengvai naudojama duomenų bazė, skirta mobiliesiems, interneto ir serverių kūrimams. Jei esate susipažinę su „Firebase“ realiuoju laiku veikiančia duomenų baze, „Firestore“ turi daug panašumų, tačiau turi skirtingą (neabejotinai deklaratyvesnę) API.

Štai keletas funkcijų, kurias „Firestore“ pateikia į lentelę:

⚡️ Lengvai gaukite duomenis realiuoju laiku

Kaip ir „Firebase“ realaus laiko duomenų bazė, „Firestore“ teikia naudingų metodų, pvz., .OnSnapshot (), todėl realiu laiku klausytis, ar jūsų duomenys yra naujoviški, labai lengva. Tai daro „Firestore“ idealų pasirinkimą projektams, kuriems suteikiama aukščiausio lygio galimybė rodyti ir naudoti naujausius duomenis (pvz., Pokalbių programas).

? „NoSQL“ duomenų bazės lankstumas

„Firestore“ yra labai lanksti užpakalinės programos galimybė, nes tai yra „NoSQL“ duomenų bazė. „NoSQL“ reiškia, kad duomenys nėra saugomi lentelėse ir stulpeliuose, kaip būtų standartinė SQL duomenų bazė. Jis sukonstruotas kaip raktų vertės saugykla, tarsi tai būtų vienas didelis „JavaScript“ objektas.

Kitaip tariant, nėra schemos ar poreikio apibūdinti, kokius duomenis saugo mūsų duomenų bazė. Kol pateiksime galiojančius raktus ir reikšmes, „Firestore“ juos saugos.

↕️ Lengvai keičiama

Vienas didelis pranašumas renkantis „Firestore“ savo duomenų bazei yra labai galinga infrastruktūra, kuria remiasi ir kuri leidžia labai lengvai išplėsti savo programą. Tiek vertikaliai, tiek horizontaliai. Nesvarbu, ar turite šimtus, ar milijonus vartotojų. „Google“ serveriai galės valdyti bet kokią apkrovą.

Trumpai tariant, „Firestore“ yra puikus pasirinkimas tiek mažoms, tiek didelėms programoms. Mažoms programoms tai galinga, nes galime daug nuveikti be daug sąrankos ir labai greitai su jomis kurti projektus. „Firestore“ dėl savo mastelio puikiai tinka dideliems projektams.

„Firestore“ nustatymas „JavaScript“ projekte

„JavaScript“ naudosime „Firestore“ SDK. Šiame cheatsheet aprašysime, kaip naudoti „Firestore“ „JavaScript“ projekto kontekste. Nepaisant to, čia aptartos sąvokos yra lengvai perkeliamos į bet kurią iš galimų „Firestore“ klientų bibliotekų.

Norėdami pradėti naudoti „Firestore“, eisime į „Firebase“ konsolę. Galite apsilankyti apsilankę adresu firebase.google.com. Norėdami prisijungti, turite turėti „Google“ paskyrą.

Kai būsime prisijungę, sukursime naują projektą ir suteiksime jam pavadinimą.

Kai bus sukurtas mūsų projektas, mes jį pasirinksime. Po to, savo projekto prietaisų skydelyje, mes pasirinksime kodo mygtuką.

Tai suteiks mums kodą, kurio reikia norint integruoti „Firestore“ į „JavaScript“ projektą.

Paprastai, jei tai nustatote bet kokioje „JavaScript“ programoje, turėsite tai įdėti į specialų failą, vadinamą firebase.js. Jei naudojate bet kurią „JavaScript“ biblioteką, kurioje yra failas „package.json“, norėsite įdiegti „Firebase“ priklausomybę su npm arba verpalais.

// with npm npm i firebase // with yarn yarn add firebase

„Firestore“ galima naudoti kliente arba serveryje. Jei naudojate „Firestore“ su „Node“, turėsite naudoti „CommonJS“ sintaksę su reikalauti. Kitu atveju, jei kliente naudojate „JavaScript“, importuosite „Firebase“ naudodami ES modulius.

// with Commonjs syntax (if using Node) const firebase = require("firebase/app"); require("firebase/firestore"); // with ES Modules (if using client-side JS, like React) import firebase from 'firebase/app'; import 'firebase/firestore'; var firebaseConfig = { apiKey: "AIzaSyDpLmM79mUqbMDBexFtOQOkSl0glxCW_ds", authDomain: "lfasdfkjkjlkjl.firebaseapp.com", databaseURL: "//lfasdlkjkjlkjl.firebaseio.com", projectId: "lfasdlkjkjlkjl", storageBucket: "lfasdlkjkjlkjl.appspot.com", messagingSenderId: "616270824980", appId: "1:616270824990:web:40c8b177c6b9729cb5110f", }; // Initialize Firebase firebase.initializeApp(firebaseConfig);

Firestore kolekcijos ir dokumentai

Norint suprasti, kaip dirbti su „Firestore“, yra du pagrindiniai terminai: dokumentai ir kolekcijos .

Documents are individual pieces of data in our database. You can think of documents to be much like simple JavaScript objects. They consist of key-value pairs, which we refer to as fields. The values of these fields can be strings, numbers, Booleans, objects, arrays, and even binary data.

document -> { key: value } 

Sets of these documents of these documents are known as collections. Collections are very much like arrays of objects. Within a collection, each document is linked to a given identifier (id).

collection -> [{ id: doc }, { id: doc }]

Managing our database with the Firestore Console

Before we can actually start working with our database we need to create it.

Within our Firebase console, go to the 'Database' tab and create your Firestore database.

Once you've done that, we will start in test mode and enable all reads and writes to our database. In other words, we will have open access to get and change data in our database. If we were to add Firebase authentication, we could restrict access only to authenticated users.

After that, we'll be taken to our database itself, where we can start creating collections and documents. The root of our database will be a series of collections, so let's make our first collection.

We can select 'Start collection' and give it an id. Every collection is going to have an id or a name. For our project, we're going to keep track of our users' favorite books. We'll give our first collection the id 'books'.

Next, we'll add our first document with our newly-created 'books' collection.

Each document is going to have an id as well, linking it to the collection in which it exists.

In most cases we're going to use an  option to give it an automatically generated ID. So we can hit the button 'auto id' to do so, after which we need to provide a field, give it a type, as well as a value.

For our first book, we'll make a 'title' field of type 'string', with the value 'The Great Gatsby', and hit save.

After that, we should see our first item in our database.

Getting data from a collection with .get()

To get access Firestore use all of the methods it provides, we use firebase.firestore(). This method need to be executed every time we want to interact with our Firestore database.

Aš rekomenduočiau sukurti specialų kintamąjį, kuriame būtų saugoma viena nuoroda į „Firestore“. Tai padės sumažinti kodo, kurį rašote savo programoje, kiekį.

const db = firebase.firestore(); 
Tačiau šioje kodo lape aš kiekvieną kartą laikysiuosi „firestore“ metodo, kad būtų kuo aiškesnis.

Norėdami nurodyti kolekciją, mes naudojame .collection()metodą ir kaip argumentą pateikiame kolekcijos ID. Norėdami gauti nuorodą į mūsų sukurtą knygų kolekciją, tiesiog įveskite eilutę „knygos“.

const booksRef = firebase.firestore().collection('books');

Norėdami gauti visus dokumento duomenis iš kolekcijos, galime susieti .get()metodą.

.get()pateikia pažadą, o tai reiškia, kad galime jį išspręsti naudodami .then()atgalinį skambutį arba galime naudoti sintaksę „async-await“, jei vykdome kodą naudodami „async“ funkciją.

Once our promises is resolved in one way or another, we get back what's known as a snapshot.

For a collection query that snapshot is going to consist of a number of individual documents. We can access them by saying snapshot.docs.

From each document, we can get the id as a separate property, and the rest of the data using the .data() method.

Here's what our entire query looks like:

const booksRef = firebase .firestore() .collection("books"); booksRef .get() .then((snapshot) => { const data = snapshot.docs.map((doc) => ({ id: doc.id, ...doc.data(), })); console.log("All data in 'books' collection", data); // [ { id: 'glMeZvPpTN1Ah31sKcnj', title: 'The Great Gatsby' } ] });

Subscribing to a collection with .onSnapshot()

The .get() method simply returns all the data within our collection.

To leverage some of Firestore's realtime capabilities we can subscribe to a collection, which gives us the current value of the documents in that collection, whenever they are updated.

Instead of using the .get() method, which is for querying a single time, we use the .onSnapshot() method.

firebase .firestore() .collection("books") .onSnapshot((snapshot) => { const data = snapshot.docs.map((doc) => ({ id: doc.id, ...doc.data(), })); console.log("All data in 'books' collection", data); });

In the code above, we're using what's known as method chaining instead of creating a separate variable to reference the collection.

What's powerful about using firestore is that we can chain a bunch of methods one after another, making for more declarative, readable code.

Within onSnapshot's callback, we get direct access to the snapshot of our collection, both now and whenever it's updated in the future. Try manually updating our one document and you'll see that .onSnapshot() is listening for any changes in this collection.

Difference between .get() and .onSnapshot()

The difference between the get and the snapshot methods is that get returns a promise, which needs to be resolved, and only then we get the snapshot data.

.onSnapshot, however, utilizes synchronous callback function, which gives us direct access to the snapshot.

This is important to keep in mind when it comes to these different methods--we have to know which of them return a promise and which are synchronous.

Unsubscribing from a collection with unsubscribe()

Note additionally that .onSnapshot() returns a function which we can use to unsubscribe and stop listening on a given collection.

This is important in cases where the user, for example, goes away from a given page where we're displaying a collection's data. Here's an example, using the library React were we are calling unsubscribe within the useEffect hook.

When we do so this is going to make sure that when our component is unmounted (no longer displayed within the context of our app) that we're no longer listening on the collection data that we're using in this component.

function App() { const [books, setBooks] = React.useState([]); React.useEffect(() => { const unsubscribe = firebase .firestore() .collection("books") .onSnapshot((snapshot) => { const data = snapshot.docs.map((doc) => ({ id: doc.id, ...doc.data(), })); setBooks(data); }); }, []); return books.map(book => ) }

Getting Individual Documents with .doc()

When it comes to getting a document within a collection., the process is just the same as getting an entire collection: we need to first create a reference to that document, and then use the get method to grab it.

After that, however, we use the .doc() method chained on to the collection method. In order to create a reference, we need to grab this id from the database if it was auto generated. After that, we can chain on .get() and resolve the promise.

const bookRef = firebase .firestore() .collection("books") .doc("glMeZvPpTN1Ah31sKcnj"); bookRef.get().then((doc) => { if (!doc.exists) return; console.log("Document data:", doc.data()); // Document data: { title: 'The Great Gatsby' } });

Notice the conditional if (!doc.exists) return; in the code above.

Once we get the document back, it's essential to check to see whether it exists.

If we don't, there'll be an error in getting our document data. The way to check and see if our document exists is by saying, if doc.exists, which returns a true or false value.

If this expression returns false, we want to return from the function or maybe throw an error. If doc.exists is true, we can get the data from doc.data.

Adding document to a collection with .add()

Next, let's move on to changing data. The easiest way to add a new document to a collection is with the .add() method.

All you need to do is select a collection reference (with .collection()) and chain on .add().

Going back to our definition of documents as being like JavaScript objects, we need to pass an object to the .add() method and specify all the fields we want to be on the document.

Let's say we want to add another book, 'Of Mice and Men':

firebase .firestore() .collection("books") .add({ title: "Of Mice and Men", }) .then((ref) => { console.log("Added doc with ID: ", ref.id); // Added doc with ID: ZzhIgLqELaoE3eSsOazu });

The .add method returns a promise and from this resolved promise, we get back a reference to the created document, which gives us information such as the created id.

The .add() method auto generates an id for us. Note that we can't use this ref directly to get data. We can however pass the ref to the doc method to create another query.

Adding a document to a collection with .set()

Another way to add a document to a collection is with the .set() method.

Where set differs from add lies in the need to specify our own id upon adding the data.

This requires chaining on the .doc() method with the id that you want to use. Also, note how when the promise is resolved from .set(), we don't get a reference to the created document:

firebase .firestore() .collection("books") .doc("another book") .set({ title: "War and Peace", }) .then(() => { console.log("Document created"); });

Additionally, when we use .set() with an existing document, it will, by default, overwrite that document.

If we want to merge, an old document with a new document instead of overwriting it, we need to pass an additional argument to .set() and provide the property merge set to true.

// use .set() to merge data with existing document, not overwrite const bookRef = firebase .firestore() .collection("books") .doc("another book"); bookRef .set({ author: "Lev Nikolaevich Tolstoy" }, { merge: true }) .then(() => { console.log("Document merged"); bookRef .get() .then(doc => { console.log("Merged document: ", doc.data()); // Merged document: { title: 'War and Peace', author: 'Lev Nikolaevich Tolstoy' } }); });

Updating existing data with .update()

When it comes to updating data we use the update method, like .add() and .set() it returns a promise.

Naudinga .update()tai, kad, skirtingai nei .set()tai neperrašys viso dokumento. Be to .set(), mums reikia nurodyti atskirą dokumentą.

Kai naudojate .update(), svarbu naudoti klaidų tvarkymą, pvz., .catch()Atgalinį skambutį, jei dokumento nėra.

const bookRef = firebase.firestore().collection("books").doc("another book"); bookRef .update({ year: 1869, }) .then(() => { console.log("Document updated"); // Document updated }) .catch((error) => { console.error("Error updating doc", error); }); 

Duomenų trynimas naudojant .delete ()

Mes galime ištrinti pateiktą dokumentų rinkinį, nurodydami jį pagal jo ID ir vykdydami .delete()paprastą metodą. Tai taip pat grąžina pažadą.

Štai pagrindinis knygos, kurios ID yra „kita knyga“, ištrynimo pavyzdys:

firebase .firestore() .collection("books") .doc("another book") .delete() .then(() => console.log("Document deleted")) // Document deleted .catch((error) => console.error("Error deleting document", error));
Atminkite, kad oficialioje „Firestore“ dokumentacijoje nerekomenduojama ištrinti visų kolekcijų, tik atskirų dokumentų.

Darbas su subkolekcijomis

Let's say that we made a misstep in creating our application, and instead of just adding books we also want to connect them to the users that made them. T

The way that we want to restructure the data is by making a collection called 'users' in the root of our database, and have 'books' be a subcollection of 'users'. This will allow users to have their own collections of books. How do we set that up?

References to the subcollection 'books' should look something like this:

const userBooksRef = firebase .firestore() .collection('users') .doc('user-id') .collection('books');

Note additionally that we can write this all within a single .collection() call using forward slashes.

The above code is equivalent to the follow, where the collection reference must have an odd number of segments. If not, Firestore will throw an error.

const userBooksRef = firebase .firestore() .collection('users/user-id/books');

To create the subcollection itself, with one document (another Steinbeck novel, 'East of Eden') run the following.

firebase.firestore().collection("users/user-1/books").add({ title: "East of Eden", });

Then, getting that newly created subcollection would look like the following based off of the user's ID.

firebase .firestore() .collection("users/user-1/books") .get() .then((snapshot) => { const data = snapshot.docs.map((doc) => ({ id: doc.id, ...doc.data(), })); console.log(data); // [ { id: 'UO07aqpw13xvlMAfAvTF', title: 'East of Eden' } ] });

Useful methods for Firestore fields

There are some useful tools that we can grab from Firestore that enables us to work with our field values a little bit easier.

For example, we can generate a timestamp for whenever a given document is created or updated with the following helper from the FieldValue property.

We can of course create our own date values using JavaScript, but using a server timestamp lets us know exactly when data is changed or created from Firestore itself.

firebase .firestore() .collection("users") .doc("user-2") .set({ created: firebase.firestore.FieldValue.serverTimestamp(), }) .then(() => { console.log("Added user"); // Added user });

Additionally, say we have a field on a document which keeps track of a certain number, say the number of books a user has created. Whenever a user creates a new book we want to increment that by one.

An easy way to do this, instead of having to first make a .get() request, is to use another field value helper called .increment():

const userRef = firebase.firestore().collection("users").doc("user-2"); userRef .set({ count: firebase.firestore.FieldValue.increment(1), }) .then(() => { console.log("Updated user"); userRef.get().then((doc) => { console.log("Updated user data: ", doc.data()); }); }); 

Querying with .where()

What if we want to get data from our collections based on certain conditions? For example, say we want to get all of the users that have submitted one or more books?

We can write such a query with the help of the .where() method. First we reference a collection and then chain on .where().

The where method takes three arguments--first, the field that we're searching on an operation, an operator, and then the value on which we want to filter our collection.

Mes galime naudoti bet kurį iš šių operatorių, o laukai, kuriuos naudojame, gali būti ir primityviosios vertės, ir masyvai.

<, <=, ==, >, >=, array-contains, in, Arbaarray-contains-any

Norėdami gauti visus vartotojus, pateikusius daugiau nei vieną knygą, galime naudoti šią užklausą.

Po to, kai .where()mums reikia grandinės .get(). Išsprendę pažadą, grįšime tai, kas vadinama „ querySnapshot“ .

Kaip ir gaunant kolekciją, galime kartoti „querySnapshot“, .map()kad gautume kiekvieno dokumento ID ir duomenis (laukus):

firebase .firestore() .collection("users") .where("count", ">=", 1) .get() .then((querySnapshot) => { const data = querySnapshot.docs.map((doc) => ({ id: doc.id, ...doc.data(), })); console.log("Users with > 1 book: ", data); // Users with > 1 book: [ { id: 'user-1', count: 1 } ] });
Atminkite, kad galite susieti kelis .where()metodus, kad sukurtumėte sudėtines užklausas.

Užklausų ribojimas ir užsakymas

Another method for effectively querying our collections is to limit them. Let's say we want to limit a given query to a certain amount of documents.

If we only want to return a few items from our query, we just need to add on the .limit() method, after a given reference.

If we wanted to do that through our query for fetching users that have submitted at least one book, it would look like the following.

const usersRef = firebase .firestore() .collection("users") .where("count", ">=", 1); usersRef.limit(3)

Another powerful feature is to order our queried data according to document fields using .orderBy().

If we want to order our created users by when they were first made, we can use the orderBy method with the 'created' field as the first argument. For the second argument, we specify whether it should be in ascending or descending order.

Norėdami, kad visi vartotojai būtų suskirstyti pagal jų sukūrimą nuo naujausių iki seniausių, galime vykdyti šią užklausą:

const usersRef = firebase .firestore() .collection("users") .where("count", ">=", 1); usersRef.orderBy("created", "desc").limit(3);

Galime grandinės .orderBy()su .limit(). Norint, kad tai veiktų tinkamai, .limit()reikia skambinti paskutiniam, o ne anksčiau .orderBy().

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