El tutorial de JavaScript + Firestore para 2020: aprender con el ejemplo

Cloud Firestore es una base de datos NoSQL sin servidor ultrarrápida, perfecta para impulsar aplicaciones web y móviles de cualquier tamaño. Obtén la guía completa para aprender Firestore, creada para mostrarte cómo usar Firestore como motor para tus propios proyectos increíbles de principio a fin.

Tabla de contenido

Introducción a Firestore

  • ¿Qué es Firestore? ¿Por qué debería usarlo?
  • Configuración de Firestore en un proyecto de JavaScript
  • Documentos y colecciones de Firestore
  • Administrar nuestra base de datos con Firebase Console

Obteniendo datos con Firestore

  • Obtener datos de una colección con .get ()
  • Suscripción a una colección con .onSnapshot ()
  • Diferencia entre .get () y .onSnapshot ()
  • Cancelar la suscripción a una colección
  • Obtener documentos individuales

Cambiar datos con Firestore

  • Agregar documento a una colección con .add ()
  • Agregar un documento a una colección con .set ()
  • Actualización de datos existentes
  • Borrando datos

Patrones esenciales

  • Trabajar con subcolecciones
  • Métodos útiles para los campos de Firestore
  • Consultando con .where ()
  • Ordenar y limitar datos

Nota: puede descargar una versión en PDF de este tutorial para poder leerlo sin conexión.

¿Qué es Firestore? ¿Por qué debería usarlo?

Firestore es una base de datos muy flexible y fácil de usar para el desarrollo móvil, web y de servidores. Si está familiarizado con la base de datos en tiempo real de Firebase, Firestore tiene muchas similitudes, pero con una API diferente (posiblemente más declarativa).

Estas son algunas de las características que Firestore trae a la mesa:

⚡️Obtenga datos fácilmente en tiempo real

Al igual que la base de datos en tiempo real de Firebase, Firestore proporciona métodos útiles como .onSnapshot () que facilitan escuchar las actualizaciones de sus datos en tiempo real. Hace de Firestore una opción ideal para proyectos que priorizan la visualización y el uso de los datos más recientes (aplicaciones de chat, por ejemplo).

? Flexibilidad como base de datos NoSQL

Firestore es una opción muy flexible para un backend porque es una base de datos NoSQL. NoSQL significa que los datos no se almacenan en tablas y columnas como lo haría una base de datos SQL estándar. Está estructurado como un almacén de valores clave, como si fuera un gran objeto de JavaScript.

En otras palabras, no hay un esquema ni es necesario describir qué datos almacenará nuestra base de datos. Siempre que proporcionemos claves y valores válidos, Firestore los almacenará.

↕️ escalable sin esfuerzo

Un gran beneficio de elegir Firestore para su base de datos es la infraestructura muy poderosa sobre la que se basa y que le permite escalar su aplicación con mucha facilidad. Tanto en vertical como en horizontal. No importa si tiene cientos o millones de usuarios. Los servidores de Google podrán manejar cualquier carga que le pongas.

En resumen, Firestore es una excelente opción para aplicaciones tanto pequeñas como grandes. Para aplicaciones pequeñas es poderoso porque podemos hacer mucho sin mucha configuración y crear proyectos muy rápidamente con ellas. Firestore es ideal para proyectos grandes debido a su escalabilidad.

Configuración de Firestore en un proyecto de JavaScript

Vamos a utilizar el SDK de Firestore para JavaScript. A lo largo de esta hoja de trucos, cubriremos cómo usar Firestore dentro del contexto de un proyecto de JavaScript. A pesar de esto, los conceptos que cubriremos aquí son fácilmente transferibles a cualquiera de las bibliotecas cliente de Firestore disponibles.

Para comenzar con Firestore, nos dirigiremos a la consola de Firebase. Puede visitarlo en firebase.google.com. Deberá tener una cuenta de Google para iniciar sesión.

Una vez que hayamos iniciado sesión, crearemos un nuevo proyecto y le daremos un nombre.

Una vez creado nuestro proyecto, lo seleccionaremos. Después de eso, en el tablero de nuestro proyecto, seleccionaremos el botón de código.

Esto nos dará el código que necesitamos para integrar Firestore con nuestro proyecto JavaScript.

Por lo general, si está configurando esto en cualquier tipo de aplicación de JavaScript, querrá ponerlo en un archivo dedicado llamado firebase.js. Si está utilizando una biblioteca de JavaScript que tiene un archivo package.json, querrá instalar la dependencia de Firebase con npm o yarn.

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

Firestore se puede utilizar en el cliente o en el servidor. Si está utilizando Firestore con Node, deberá utilizar la sintaxis CommonJS con require. De lo contrario, si está usando JavaScript en el cliente, importará firebase usando los módulos ES.

// 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);

Colecciones y documentos de Firestore

Hay dos términos clave que son esenciales para comprender cómo trabajar con Firestore: documentos y colecciones .

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.

Recomendaría crear una variable dedicada para almacenar una única referencia a Firestore. Hacerlo ayuda a reducir la cantidad de código que escribe en su aplicación.

const db = firebase.firestore(); 
En esta hoja de trucos, sin embargo, me limitaré a usar el método firestore cada vez para ser lo más claro posible.

Para hacer referencia a una colección, usamos el .collection()método y proporcionamos la identificación de una colección como argumento. Para obtener una referencia a la colección de libros que creamos, simplemente pase la cadena 'libros'.

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

Para obtener todos los datos del documento de una colección, podemos encadenar el .get()método.

.get()devuelve una promesa, lo que significa que podemos resolverla usando una .then()devolución de llamada o podemos usar la sintaxis async-await si estamos ejecutando nuestro código dentro de una función async.

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.

Lo que es útil sobre el uso .update()es que, a diferencia .set(), no sobrescribirá todo el documento. También como .set(), necesitamos hacer referencia a un documento individual.

Cuando lo usa .update(), es importante usar algún manejo de errores, como la .catch()devolución de llamada en caso de que el documento no exista.

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); }); 

Eliminar datos con .delete ()

Podemos eliminar una colección de documentos determinada haciendo referencia a ella por su id y ejecutando el .delete()método, así de simple. También devuelve una promesa.

A continuación, se muestra un ejemplo básico de cómo eliminar un libro con la identificación "otro libro":

firebase .firestore() .collection("books") .doc("another book") .delete() .then(() => console.log("Document deleted")) // Document deleted .catch((error) => console.error("Error deleting document", error));
Tenga en cuenta que la documentación oficial de Firestore no recomienda eliminar colecciones completas, solo documentos individuales.

Trabajar con subcolecciones

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.

Podemos usar cualquiera de los siguientes operadores y los campos que usamos pueden ser tanto valores primitivos como matrices.

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

Para obtener todos los usuarios que han enviado más de un libro, podemos utilizar la siguiente consulta.

Después .where()tenemos que encadenarnos .get(). Al resolver nuestra promesa, recuperamos lo que se conoce como querySnapshot .

Al igual que obtener una colección, podemos iterar sobre querySnapshot con .map()para obtener cada identificación de documento y datos (campos):

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 } ] });
Tenga en cuenta que puede encadenar varios .where()métodos para crear consultas compuestas.

Limitar y ordenar consultas

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.

To get all of the users ordered by when they were created from newest to oldest, we can execute the following query:

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

We can chain .orderBy() with .limit(). For this to work properly, .limit() should be called last and not before .orderBy().

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