urql

Server-side Rendering

In server-side rendered applications we often need to set our application up so that data will be fetched on the server-side and later sent down to the client for hydration. urql supports this through the ssrExchange.

The SSR Exchange

The ssrExchange has two functions. On the server-side it's able to gather all results as they're being fetched, which can then be serialized and sent to the client. On the client-side it's able to use these serialized results to rehydrate and render the application without refetching this data.

To start out with the ssrExchange we have to add the exchange to our Client:

import { createClient, dedupExchange, cacheExchange, fetchExchange, ssrExchange } from '@urql/core';


const isServerSide = typeof window === 'undefined';


// The `ssrExchange` must be initialized with `isClient` and `initialState`
const ssr = ssrExchange({
  isClient: !isServerSide,
  initialState: !isServerSide ? window.__URQL_DATA__ : undefined,
});


const client = createClient({
  exchanges: [
    dedupExchange,
    cacheExchange,
    ssr, // Add `ssr` in front of the `fetchExchange`
    fetchExchange,
  ],
});

The ssrExchange must be initialized with the isClient and initialState options. The isClient option tells the exchange whether it's on the server- or client-side. In our example we use typeof window to determine this, but in Webpack environments you may also be able to use process.browser.

Optionally, we may also choose to enable staleWhileRevalidate. When enabled this flag will ensure that although a result may have been rehydrated from our SSR result, another refetch network-only operation will be issued, to update stale data. This is useful for statically generated sites (SSG) that may ship stale data to our application initially.

The initialState option should be set to the serialized data you retrieve on your server-side. This data may be retrieved using methods on ssrExchange(). You can retrieve the serialized data after server-side rendering using ssr.extractData():

// Extract and serialise the data like so from the `ssr` instance
// we've previously created by calling `ssrExchange()`
const data = JSON.stringify(ssr.extractData());


const markup = ''; // The render code for our framework goes here


const html = `
<html>
  <body>
    <div id="root">${markup}</div>
    <script>
      window.__URQL_DATA__ = JSON.parse(${data});
    </script>
  </body>
</html>
`;

This will provide __URQL_DATA__ globally, which we've used in our first example to inject data into the ssrExchange on the client-side.

Alternatively you can also call restoreData as long as this call happens synchronously before the client starts receiving queries.

const isServerSide = typeof window === 'undefined';
const ssr = ssrExchange({ isClient: !isServerSide });


if (!isServerSide) {
  ssr.restoreData(window.__URQL_DATA__);
}

Using react-ssr-prepass

In the previous examples we've set up the ssrExchange, however with React this still requires us to manually execute our queries before rendering a server-side React app using renderToString or renderToNodeStream.

For React, urql has a "Suspense mode" that allows data fetching to interrupt rendering. However, Suspense is not supported by React during server-side rendering.

Using the react-ssr-prepass package however, we can implement a prerendering step before we let React server-side render, which allows us to automatically fetch all data that the app requires with Suspense. This technique is commonly referred to as a "two-pass approach", since our React element is traversed twice.

To set this up, first we'll install react-ssr-prepass. It has a peer dependency on react-is and react.

yarn add react-ssr-prepass react-is react-dom
# or
npm install --save react-ssr-prepass react-is react-dom

Next, we'll modify our server-side code and add react-ssr-prepass in front of renderToString.

import { renderToString } from 'react-dom/server';
import prepass from 'react-ssr-prepass';


import {
  createClient,
  dedupExchange,
  cacheExchange,
  fetchExchange,
  ssrExchange
} from 'urql';


const handleRequest = async (req, res) => {
  // ...
  const ssr = ssrExchange({ isClient: false });


  const client createClient({
    suspense: true, // This activates urql's Suspense mode on the server-side
    exchanges: [dedupExchange, cacheExchange, ssr, fetchExchange]
  });


  const element = (
    <Provider value={client}>
      <App />
    </Provider>
  );


  // Using `react-ssr-prepass` this prefetches all data
  await prepass(element);
  // This is the usual React SSR rendering code
  const markup = renderToString(element);
  // Extract the data after prepass and rendering
  const data = JSON.stringify(ssr.extractData());


  res.status(200).send(`
    <html>
      <body>
        <div id="root">${markup}</div>
        <script>
          window.__URQL_DATA__ = JSON.parse(${data});
        </script>
      </body>
    </html>
  `);
};

It's important to set enable the suspense option on the Client, which switches it to support React suspense.

With Preact

If you're using Preact instead of React, there's a drop-in replacement package for react-ssr-prepass, which is called preact-ssr-prepass. It only has a peer dependency on Preact, and we can install it like so:

yarn add preact-ssr-prepass preact
# or
npm install --save preact-ssr-prepass preact

All above examples for react-ssr-prepass will still be the same, except that instead of using the urql package we'll have to import from @urql/preact, and instead of react-ssr-prepass we'll have to import from. preact-ssr-prepass.

Next.js

If you're using Next.js you can save yourself a lot of work by using next-urql. The next-urql package includes setup for react-ssr-prepass already, which automates a lot of the complexity of setting up server-side rendering with urql.

We have a custom integration with Next.js, being next-urql this integration contains convenience methods specifically for Next.js. These will simplify the above setup for SSR.

To set up next-urql, first we'll install next-urql with react-is and urql as peer dependencies:

yarn add next-urql react-is urql graphql
# or
npm install --save next-urql react-is urql graphql

The peer dependency on react-is is inherited from react-ssr-prepass requiring it.

Note that if you are using Next before v9.4 you'll need to polyfill fetch, this can be done through isomorphic-unfetch.

We're now able to wrap any page or _app.js using the withUrqlClient higher-order component. If we wrap _app.js we won't have to wrap any individual page, but we also won't be able to make use of Next's "Automatic Static Optimization".

// pages/index.js
import React from 'react';
import Head from 'next/head';
import { useQuery } from 'urql';
import { withUrqlClient } from 'next-urql';


const Index = () => {
  const [result] = useQuery({
    query: '{ test }',
  });


  // ...
};


export default withUrqlClient((_ssrExchange, ctx) => ({
  // ...add your Client options here
  url: 'http://localhost:3000/graphql',
}))(Index);

This will automatically set up server-side rendering on the page. The withUrqlClient higher-order component function accepts the usual Client options as an argument. This may either just be an object, or a function that receives the Next.js' getInitialProps context.

One added caveat is that these options may not include the exchanges option because next-urql injects the ssrExchange automatically at the right location. If you're setting up custom exchanges you'll need to instead provide them in the exchanges property of the returned client object.

import { dedupExchange, cacheExchange, fetchExchange } from '@urql/core';


import { withUrqlClient } from 'next-urql';


export default withUrqlClient(ssrExchange => ({
  url: 'http://localhost:3000/graphql',
  exchanges: [dedupExchange, cacheExchange, ssrExchange, fetchExchange],
}))(Index);

Unless the component that is being wrapped already has a getInitialProps method, next-urql won't add its own SSR logic, which automatically fetches queries during server-side rendering. This can be explicitly enabled by passing the { ssr: true } option as a second argument to withUrqlClient.

When you are using getStaticProps, getServerSideProps, or getStaticPaths, you should opt-out of Suspense by setting the neverSuspend option to true in your withUrqlClient configuration. During the prepass of your component tree next-urql can't know how these functions will alter the props passed to your page component. This injection could change the variables used in your useQuery. This will lead to error being thrown during the subsequent toString pass, which isn't supported in React 16.

Using getStaticProps or getServerSideProps

By default withUrqlClient will add getInitialProps to the component you're wrapping it in, this however excludes us from using getStaticProps and getServerSideProps. However we can enable this, let's look at an example:

import { withUrqlClient, initUrqlClient } from 'next-urql';
import { ssrExchange, dedupExchange, cacheExchange, fetchExchange, useQuery } from 'urql';


const TODOS_QUERY = `
  query { todos { id text } }
`;


function Todos() {
  const [res] = useQuery({ query: TODOS_QUERY });
  return (
    <div>
      {res.data.todos.map(todo => (
        <div key={todo.id}>
          {todo.id} - {todo.text}
        </div>
      ))}
    </div>
  );
}


export async function getStaticProps(ctx) {
  const ssrCache = ssrExchange({ isClient: false });
  const client = initUrqlClient({
    url: 'your-url',
    exchanges: [dedupExchange, cacheExchange, ssrCache, fetchExchange],
  });


  // This query is used to populate the cache for the query
  // used on this page.
  await client.query(TODOS_QUERY).toPromise();


  return {
    props: {
      // urqlState is a keyword here so withUrqlClient can pick it up.
      urqlState: ssrCache.extractData(),
    },
    revalidate: 600,
  };
}


export default withUrqlClient(
  ssr => ({
    url: 'your-url',
  }),
  { ssr: false } // Important so we don't wrap our component in getInitialProps
)(Todos);

The above example will make sure the page is rendered as a static-page, it's important that you fully pre-populate your cache so in our case we were only interested in getting our todos, if there are child components relying on data you'll have to make sure these are fetched as well.

Stale While Revalidate

If we choose to use Next's static site generation (SSG or ISG) we may be embedding data in our initial payload that's stale on the client. In this case, we may want to update this data immediately after rehydration. We can pass staleWhileRevalidate: true to withUrqlClient's second option argument to Switch it to a mode where it'll refresh its rehydrated data immediately by issuing another network request.

export default withUrqlClient(
  ssr => ({
    url: 'your-url',
  }),
  { staleWhileRevalidate: true }
)(...);

Now, although on rehydration we'll receive the stale data from our ssrExchange first, it'll also immediately issue another network-only operation to update the data. During this revalidation our stale results will be marked using result.stale. While this is similar to what we see with cache-and-network without server-side rendering, it isn't quite the same. Changing the request policy wouldn't actually refetch our data on rehydration as the ssrExchange is simply a replacement of a full network request. Hence, this flag allows us to treat this case separately.

Resetting the client instance

In rare scenario's you possibly will have to reset the client instance (reset all cache, ...), this is an uncommon scenario, and we consider it "unsafe" so evaluate this carefully for yourself.

When this does seem like the appropriate solution any component wrapped with withUrqlClient will receive the resetUrqlClient property, when invoked this will create a new top-level client and reset all prior operations.

Vue Suspense

In Vue 3 a new feature was introduced that natively allows components to suspend while data is loading, which works universally on the server and on the client, where a replacement loading template is rendered on a parent while data is loading.

We've previously seen how we can change our usage of useQuery's PromiseLike result to make use of Vue Suspense on the "Queries" page.

Any component's setup() function can be updated to instead be an async setup() function, in other words, to return a Promise instead of directly returning its data. This means that we can update any setup() function to make use of Suspense.

On the server-side we can then use @vue/server-renderer's renderToString, which will return a Promise that resolves when all suspense-related loading is completed.

import { createSSRApp } = from 'vue'
import { renderToString } from '@vue/server-renderer';


import urql, {
  createClient,
  dedupExchange,
  cacheExchange,
  fetchExchange,
  ssrExchange
} from '@urql/vue';


const handleRequest = async (req, res) => {
  // This is where we'll put our root component
  const app = createSSRApp(Root)


  // NOTE: All we care about here is that the SSR Exchange is included
  const ssr = ssrExchange({ isClient: false });
  app.use(urql, {
    exchanges: [dedupExchange, cacheExchange, ssr, fetchExchange]
  });


  const markup = await renderToString(app);


  const data = JSON.stringify(ssr.extractData());


  res.status(200).send(`
    <html>
      <body>
        <div id="root">${markup}</div>
        <script>
          window.__URQL_DATA__ = JSON.parse(${data});
        </script>
      </body>
    </html>
  `);
};

This effectively renders our Vue app on the server-side and provides the client-side data for rehydration that we've set up in the above SSR Exchange section to use.