React + Apollo-vejledningen til 2020 (eksempler fra den virkelige verden)

Hvis du vil oprette apps med React og GraphQL, er Apollo det bibliotek, du skal bruge.

Jeg har sammensat et omfattende cheatsheet, der gennemgår alle kernekoncepterne i Apollo-biblioteket og viser dig, hvordan du bruger det med React fra front til bagside.

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En stor del af dette cheatsheet er baseret på den app, der er bygget i React + GraphQL 2020 Crash Course.

Hvis du vil have flere praktiske videotimer plus se, hvordan du bygger apps med React, GraphQL og Apollo, kan du se kurset lige her.

Bemærk: Dette cheatsheet antager fortrolighed med React og GraphQL. Hvis du har brug for en hurtig opdatering af GraphQL, og hvordan du skriver det, er en stor ressource det officielle GraphQL-websted.

Indholdsfortegnelse

Kom godt i gang

  • Hvad er Apollo, og hvorfor har vi brug for det?
  • Opsætning af Apollo Client
  • Oprettelse af en ny Apollo-klient
  • Tilbyde klienten at reagere på komponenter
  • Brug af klienten direkte
  • Skrivning af GraphQL i .js-filer med gql

Core Apollo React kroge

  • useQuery Hook
  • useLazyQuery Hook
  • useMutation Hook
  • useSubscription Hook

Væsentlige opskrifter

  • Manuel indstilling af hentningspolitikken
  • Opdatering af cachen efter en mutation
  • Hentning af forespørgsler med useQuery
  • Hentning af forespørgsler med useMutation
  • Adgang til klienten med useApolloClient

Hvad er Apollo, og hvorfor har vi brug for det?

Apollo er et bibliotek, der samler to utroligt nyttige teknologier, der bruges til at opbygge web- og mobilapps: React og GraphQL.

React blev lavet for at skabe gode brugeroplevelser med JavaScript. GraphQL er et meget ligetil og deklarativt nyt sprog, der lettere og mere effektivt kan hente og ændre data, hvad enten det er fra en database eller endda fra statiske filer.

Apollo er limen, der binder disse to værktøjer sammen. Plus det gør arbejdet med React og GraphQL meget lettere ved at give os en masse tilpassede React-kroge og funktioner, der gør det muligt for os både at skrive GraphQL-operationer og udføre dem med JavaScript-kode.

Vi dækker disse funktioner i dybden i løbet af denne vejledning.

Apollo Client grundlæggende opsætning

Hvis du starter et projekt med en React-skabelon som Create React App, skal du installere følgende som dine basale afhængigheder for at komme i gang med Apollo Client:

// with npm: npm i @apollo/react-hooks apollo-boost graphql // with yarn: yarn add @apollo/react-hooks apollo-boost graphql 

@apollo/react-hooks giver os React-kroge, der gør det bedre at udføre vores operationer og arbejde med Apollo-klienten

apollo-boost hjælper os med at oprette klienten sammen med at analysere vores GraphQL-operationer

graphql tager sig også af parsing af GraphQL-operationerne (sammen med gql)

Apollo Client + abonnementsopsætning

For at bruge alle former for GraphQL-operationer (forespørgsler, mutationer og abonnementer) er vi nødt til at installere mere specifikke afhængigheder sammenlignet med bare apollo-boost:

// with npm: npm i @apollo/react-hooks apollo-client graphql graphql-tag apollo-cache-inmemory apollo-link-ws // with yarn: yarn add @apollo/react-hooks apollo-client graphql graphql-tag apollo-cache-inmemory apollo-link-ws 

apollo-client giver os klienten direkte i stedet for fra apollo-boost

graphql-tager integreret i apollo-boost, men ikke inkluderet iapollo-client

apollo-cache-inmemoryer nødvendigt for at opsætte vores egen cache (som apollo-boosttil sammenligning automatisk gør)

apollo-link-ws er nødvendig til kommunikation via websockets, hvilke abonnementer kræver

Oprettelse af en ny Apollo Client (grundlæggende opsætning)

Den mest enkle opsætning til oprettelse af en Apollo-klient er ved at starte en ny klient og levere netop den uriejendom, som vil være dit GraphQL-slutpunkt:

import ApolloClient from "apollo-boost"; const client = new ApolloClient({ uri: "//your-graphql-endpoint.com/api/graphql", }); 

apollo-boostblev udviklet for at gøre ting som at oprette en Apollo Client så let som muligt. Det, der mangler for tiden, er imidlertid understøttelse af GraphQL-abonnementer over en websocket-forbindelse.

Som standard udfører den operationerne via en http-forbindelse (som du kan se gennem vores leverede uri ovenfor).

Kort sagt, brug apollo-boosttil at oprette din klient, hvis du kun har brug for at udføre forespørgsler og mutationer i din app.

It setups an in-memory cache by default, which is helpful for storing our app data locally. We can read from and write to our cache to prevent having to execute our queries after our data is updated. We'll cover how to do that a bit later.

Creating a new Apollo Client (+ subscriptions setup)

Subscriptions are useful for more easily displaying the result of data changes (through mutations) in our app.

Generally speaking, we use subscriptions as an improved kind of query. Subscriptions use a websocket connection to 'subscribe' to updates and data, enabling new or updated data to be immediately displayed to our users without having to reexecute queries or update the cache.

import ApolloClient from "apollo-client"; import { WebSocketLink } from "apollo-link-ws"; import { InMemoryCache } from "apollo-cache-inmemory"; const client = new ApolloClient({ link: new WebSocketLink({ uri: "wss://your-graphql-endpoint.com/v1/graphql", options: { reconnect: true, connectionParams: { headers: { Authorization: "Bearer yourauthtoken", }, }, }, }), cache: new InMemoryCache(), }); 

Providing the client to React components

After creating a new client, passing it to all components is essential in order to be able to use it within our components to perform all of the available GraphQL operations.

The client is provided to the entire component tree using React Context, but instead of creating our own context, we import a special context provider from @apollo/react-hooks called ApolloProvider . We can see how it differs from the regular React Context due to it having a special prop, client, specifically made to accept the created client.

Note that all of this setup should be done in your index.js or App.js file (wherever your Routes declared) so that the Provider can be wrapped around all of your components.

import { ApolloProvider } from "@apollo/react-hooks"; const rootElement = document.getElementById("root"); ReactDOM.render(           , rootElement ); 

Using the client directly

The Apollo client is most important part of the library due to the fact that it is responsible for executing all of the GraphQL operations that we want to perform with React.

We can use the created client directly to perform any operation we like. It has methods corresponding to queries (client.query()), mutations (client.mutate()), and subscriptions (client.subscribe()).

Each method accepts an object and it's own corresponding properties:

// executing queries client .query({ query: GET_POSTS, variables: { limit: 5 }, }) .then((response) => console.log(response.data)) .catch((err) => console.error(err)); // executing mutations client .mutate({ mutation: CREATE_POST, variables: { title: "Hello", body: "World" }, }) .then((response) => console.log(response.data)) .catch((err) => console.error(err)); // executing subscriptions client .subscribe({ subscription: GET_POST, variables: { id: "8883346c-6dc3-4753-95da-0cc0df750721" }, }) .then((response) => console.log(response.data)) .catch((err) => console.error(err)); 

Using the client directly can be a bit tricky, however, since in making a request, it returns a promise. To resolve each promise, we either need .then() and .catch() callbacks as above or to await each promise within a function declared with the async keyword.

Writing GraphQL operations in .js files (gql)

Notice above that I didn't specify the contents of the variables GET_POSTS, CREATE_POST, and GET_POST.

They are the operations written in the GraphQL syntax which specify how to perform the query, mutation, and subscription respectively. They are what we would write in any GraphiQL console to get and change data.

The issue here, however, is that we can't write and execute GraphQL instructions in JavaScript (.js) files, like our React code has to live in.

To parse the GraphQL operations, we use a special function called a tagged template literal to allow us to express them as JavaScript strings. This function is named gql.

 // if using apollo-boost import { gql } from "apollo-boost"; // else, you can use a dedicated package graphql-tag import gql from "graphql-tag"; // query const GET_POSTS = gql` query GetPosts($limit: Int) { posts(limit: $limit) { id body title createdAt } } `; // mutation const CREATE_POST = gql` mutation CreatePost($title: String!, $body: String!) { insert_posts(objects: { title: $title, body: $body }) { affected_rows } } `; // subscription const GET_POST = gql` subscription GetPost($id: uuid!) { posts(where: { id: { _eq: $id } }) { id body title createdAt } } `; 

useQuery Hook

The useQuery hook is arguably the most convenient way of performing a GraphQL query, considering that it doesn't return a promise that needs to be resolved.

It is called at the top of any function component (as all hooks should be) and receives as a first required argument—a query parsed with gql.

It is best used when you have queries that should be executed immediately, when a component is rendered, such as a list of data which the user would want to see immediately when the page loads.

useQuery returns an object from which we can easily destructure the values that we need. Upon executing a query, there are three primary values will need to use within every component in which we fetch data. They are loading, error, and data.

const GET_POSTS = gql` query GetPosts($limit: Int) { posts(limit: $limit) { id body title createdAt } } `; function App() { const { loading, error, data } = useQuery(GET_POSTS, { variables: { limit: 5 }, }); if (loading) return Loading... ; if (error) return Error! ; return data.posts.map((post) => ); } 

Before we can display the data that we're fetching, we need to handle when we're loading (when loading is set to true) and we are attempting to fetch the data.

At that point, we display a div with the text 'Loading' or a loading spinner. We also need to handle the possibility that there is an error in fetching our query, such as if there's a network error or if we made a mistake in writing our query (syntax error).

Once we're done loading and there's no error, we can use our data in our component, usually to display to our users (as we are in the example above).

There are other values which we can destructure from the object that useQuery returns, but you'll need loading, error, and data in virtually every component where you execute useQuery. You can see a full list of all of the data we can get back from useQuery here.

useLazyQuery Hook

The useLazyQuery hook provides another way to perform a query, which is intended to be executed at some time after the component is rendered or in response to a given data change.

useLazyQuery is very useful for things that happen at any unknown point of time, such as in response to a user's search operation.

function Search() { const [query, setQuery] = React.useState(""); const [searchPosts, { data }] = useLazyQuery(SEARCH_POSTS, { variables: { query: `%${query}%` }, }); const [results, setResults] = React.useState([]); React.useEffect(() => { if (!query) return; // function for executing query doesn't return a promise searchPosts(); if (data) { setResults(data.posts); } }, [query, data, searchPosts]); if (called && loading) return Loading... ; return results.map((result) => (  )); } 

useLazyQuery differs from useQuery, first of all, in what's returned from the hook. It returns an array which we can destructure, instead of an object.

Since we want to perform this query sometime after the component is mounted, the first element that we can destructure is a function which you can call to perform that query when you choose. This query function is named searchPosts in the example above.

The second destructured value in the array is an object, which we can use object destructuring on and from which we can get all of the same

properties as we did from useQuery, such as loading, error, and data.

We also get an important property named called,

which tells us if we've actually called this function to perform our query.

In that case, if called is true and loading is true, we want to

return "Loading..." instead of our actual data, because are waiting for the data to be returned. This is how useLazyQuery handles fetching data in a synchronous way without any promises.

Note that we again pass any required variables for the query operation as a property, variables, to the second argument. However, if we need, we can pass those variables on an object provided to the query function itself.

useMutation Hook

Now that we know how to execute lazy queries, we know exactly how to work with the useMutation hook.

Like the useLazyQuery hook, it returns an array which we can destructure into its two elements. In the first element, we get back a function, which in this case, we can call it to perform our mutation operation. For next element, we can again destructure an object which returns to us loading, error and data.

import { useMutation } from "@apollo/react-hooks"; import { gql } from "apollo-boost"; const CREATE_POST = gql` mutation CreatePost($title: String!, $body: String!) { insert_posts(objects: { body: $body, title: $title }) { affected_rows } } `; function NewPost() { const [title, setTitle] = React.useState(""); const [body, setBody] = React.useState(""); const [createPost, { loading, error }] = useMutation(CREATE_POST); function handleCreatePost(event) { event.preventDefault(); // the mutate function also doesn't return a promise createPost({ variables: { title, body } }); } return ( 

New Post

setTitle(event.target.value)} /> setBody(event.target.value)} /> Submit {error &&

{error.message}

} ); }

Unlike with queries, however, we don't use loading or error in order to conditionally render something. We generally use loading in such situations as when we're submitting a form to prevent it being submitted multiple times, to avoid executing the same mutation needlessly (as you can see in the example above).

We use error to display what goes wrong with our mutation to our users. If for example, some required values to our mutation are not provided, we can easily use that error data to conditionally render an error message within the page so the user can hopefully fix what's going wrong.

As compared to passing variables to the second argument of useMutation, we can access a couple of useful callbacks when certain things take place, such as when the mutation is completed and when there is an error. These callbacks are named onCompleted and onError.

The onCompleted callback gives us access to the returned mutation data and it's very helpful to do something when the mutation is done, such as going to a different page. The onError callback gives us the returned error when there is a problem with the mutation and gives us other patterns for handling our errors.

const [createPost, { loading, error }] = useMutation(CREATE_POST, { onCompleted: (data) => console.log("Data from mutation", data), onError: (error) => console.error("Error creating a post", error), }); 

useSubscription Hook

The useSubscription hook works just like the useQuery hook.

useSubscription returns an object that we can destructure, that includes the same properties, loading, data, and error.

It executes our subscription immediately when the component is rendered. This means we need to handle loading and error states, and only afterwards display/use our data.

import { useSubscription } from "@apollo/react-hooks"; import gql from "graphql-tag"; const GET_POST = gql` subscription GetPost($id: uuid!) { posts(where: { id: { _eq: $id } }) { id body title createdAt } } `; // where id comes from route params -> /post/:id function PostPage({ id }) { const { loading, error, data } = useSubscription(GET_POST, { variables: { id }, // shouldResubscribe: true (default: false) // onSubscriptionData: data => console.log('new data', data) // fetchPolicy: 'network-only' (default: 'cache-first') }); if (loading) return Loading... ; if (error) return Error! ; const post = data.posts[0]; return ( 

{post.title}

{post.body}

); }

Just like useQuery, useLazyQuery and useMutation, useSubscription accepts variables as a property provided on the second argument.

It also accepts, however, some useful properties such as shouldResubscribe. This is a boolean value, which will allow our subscription to automatically resubscribe, when our props change. This is useful for when we're passing variables to our you subscription hub props that we know will change.

Additionally, we have a callback function called onSubscriptionData, which enables us to call a function whenever the subscription hook receives new data. Finally, we can set the fetchPolicy, which defaults to 'cache-first'.

Manually Setting the Fetch Policy

What can be very useful about Apollo is that it comes with its own cache, which it uses to manage the data that we query from our GraphQL endpoint.

Sometimes, however, we find that due to this cache, things aren't updated in the UI in the way that we want.

In many cases we don't, as in the example below, where we are editing a post on the edit page, and then after editing our post, we navigate to the home page to see it in a list of all posts, but we see the old data instead:

// route: /edit/:postId function EditPost({ id }) { const { loading, data } = useQuery(GET_POST, { variables: { id } }); const [title, setTitle] = React.useState(loading ? data?.posts[0].title : ""); const [body, setBody] = React.useState(loading ? data?.posts[0].body : ""); const [updatePost] = useMutation(UPDATE_POST, { // after updating the post, we go to the home page onCompleted: () => history.push("/"), }); function handleUpdatePost(event) { event.preventDefault(); updatePost({ variables: { title, body, id } }); } return (   setTitle(event.target.value)} defaultValue={title} />  setBody(event.target.value)} defaultValue={body} /> Submit  ); } // route: / (homepage) function App() { const { loading, error, data } = useQuery(GET_POSTS, { variables: { limit: 5 }, }); if (loading) return Loading... ; if (error) return Error! ; // updated post not displayed, still see old data return data.posts.map((post) => ); } 

This not only due to the Apollo cache, but also the instructions for what data the query should fetch. We can changed how the query is fetched by using the fetchPolicy property.

By default, the fetchPolicy is set to 'cache-first'. It's going to try to look at the cache to get our data instead of getting it from the network.

An easy way to fix this problem of not seeing new data is to change the fetch policy. However, this approach is not ideal from a performance standpoint, because it requires making an additional request (using the cache directly does not, because it is local data).

There are many different options for the fetch policy listed below:

{ fetchPolicy: "cache-first"; // default /* cache-and-network cache-first cache-only network-only no-cache standby */ } 

I won't go into what each policy does exactly, but to solve our immediate problem, if you always want a query to get the latest data by requesting it from the network, we set fetchPolicy to 'network-first'.

const { loading, error, data } = useQuery(GET_POSTS, { variables: { limit: 5 }, fetchPolicy: "network-first" }); 

Updating the cache upon a mutation

Instead of bypassing the cache by changing the fetch policy of useQuery, let's attempt to fix this problem by manually updating the cache.

When performing a mutation with useMutation. We have access to another callback, known as update.

update gives us direct access to the cache as well as the data that is returned from a successful mutation. This enables us to read a given query from the cache, take that new data and write the new data to the query, which will then update what the user sees.

Working with the cache manually is a tricky process that a lot of people tend to avoid, but it's very helpful because it saves some time and resources by not having to perform the same request multiple times to update the cache manually.

function EditPost({ id }) { const [updatePost] = useMutation(UPDATE_POST, { update: (cache, data) => { const { posts } = cache.readQuery(GET_POSTS); const newPost = data.update_posts.returning; const updatedPosts = posts.map((post) => post.id === id ? newPost : post ); cache.writeQuery({ query: GET_POSTS, data: { posts: updatedPosts } }); }, onCompleted: () => history.push("/"), }); // ... } 

We first want to read the query and get the previous data from it. Then we need to take the new data. In this case, to find the post with a given id and replace it with newPost data, otherwise have it be the previous data, and then write that data back to the same query, making sure that it has the same data structure as before.

After all this, whenever we edit a post and are navigated back to the home page, we should see that new post data.

Refetching queries with useQuery

Let's say we display a list of posts using a GET_POSTS query and are deleting one of them with a DELETE_POST mutation.

When a user deletes a post, what do we want to happen?

Naturally, we want it to be removed from the list, both the data and what is displayed to the users. When a mutation is performed, however, the query doesn't know that the data is changed.

There are a few ways of updating what we see, but one approach is to reexecute the query.

We can do so by grabbing the refetch function which we can destructure from the object returned by the useQuery hook and pass it down to the mutation to be executed when it is completed, using the onCompleted callback function:

function Posts() { const { loading, data, refetch } = useQuery(GET_POSTS); if (loading) return Loading... ; return data.posts.map((post) => (  )); } function Post({ post, refetch }) { const [deletePost] = useMutation(DELETE_POST, { onCompleted: () => refetch(), }); function handleDeletePost(id) { if (window.confirm("Are you sure you want to delete this post?")) { deletePost({ variables: { id } }); } } return ( 

{post.title}

{post.body}

handleDeletePost(post.id)}>Delete ); }

Refetching Queries with useMutation

Note that we can also utilize the useMutation hook to reexecute our queries through an argument provided to the mutate function, called refetchQueries.

It accepts an array of queries that we want to refetch after a mutation is performed. Each queries is provided within an object, just like we would provide it to client.query(), and consists of a query property and a variables property.

Here is a minimal example to refetch our GET_POSTS query after a new post is created:

function NewPost() { const [createPost] = useMutation(CREATE_POST, { refetchQueries: [ { query: GET_POSTS, variables: { limit: 5 } } ], }); // ... } 

Using the client with useApolloClient

We can get access to the client across our components with the help of a special hook called use Apollo client. This execute the hook at the top of our function component and we get back the client itself.

function Logout() { const client = useApolloClient(); // client is the same as what we created with new ApolloClient() function handleLogout() { // handle logging out user, then clear stored data logoutUser(); client.resetStore().then(() => console.log("logged out!")); /* Be aware that .resetStore() is async */ } return Logout; } 

And from there we can execute all the same queries, mutations, and subscriptions.

Note that there are a ton more features that come with methods that come with the client. Using the client, we can also write and read data to and from the cache that Apollo sets up (using client.readData() and client.writeData()).

Working with the Apollo cache deserves its own crash course in itself. A great benefit of working with Apollo is that we can also use it as a state management system to replace solutions like Redux for our global state. If you want to learn more about using Apollo to manage global app state you can check out the following link.

I attempted to make this cheatsheet as comprehensive as possible, though it still leaves out many Apollo features that are worth investigating.

If you want to more about Apollo, be sure to check out the official Apollo documentation.

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