Apollo Client

Apollo Client is the client-side counterpart to Apollo Server. We use it for managing queries and mutations from the frontend to our Apollo GraphQL server. It is specifically designed to work with React.

Initializing the client

We initialise the client and set-up in memory caching to reduce network requests:

const client = new ApolloClient({
  uri: "http://localhost:4000",
  cache: new InMemoryCache(),
});

The uri property must match the location of our Apollo server.

Utilising the provider

Apollo Provides a top level application context that we can wrap our React app in. This will provide access to the client object from anywhere within the app, eg:

ReactDOM.render(
  <ApolloProvider client={client}>
    <GlobalStyles />
    <Pages />
  </ApolloProvider>,
  document.getElementById("root")
);

Running a query

Query constants

To run a query against our server we must define a query contant first. We use a gql literal again:

import { gql } from "@apollo/client";
const TRACKS = gql`
  query GetTracks {
    tracksForHome {
      id
      title
      thumbnail
      length
      modulesCount
      author {
        name
        photo
      }
    }
  }
`;

The convention is to name the query constant in ALL_CAPS.

Note that the name of the query on the client doesn't have to match the query type defined in the schema however it should reference it on the second line (`tracksFormHome)

`useQuery` hook

The useQuery hook provides a straightforward wrapper for sending queries and receiving data back from the server.

When a component renders, useQuery returns an object from the Apollo Client that contains loading, error, and data properties.

const { loading, error, data } = useQuery(TRACKS);

const Tracks = () => {
  const { loading, error, data } = useQuery(TRACKS);

  if (loading) return "Loading...";

  if (error) return `Error! ${error.message}`;

  return <Layout grid>{JSON.stringify(data)}</Layout>;
};

We destructure the loading, error, data variables that are returned from the hook
We pass in our query constant as an argument.
In the example we just render the serialized data but we could of course pass the data as a prop and map through it in an embedded child component.

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