Overview

When receiving queries from a client, the router takes on the role of a traditional GraphQL server. To reduce the amount of data sent over the network, clients can use APQ to send the router an operation hash in place of the entire operation string.

In this lesson, we will:

• Walk through how the router validates and processes APQ from a client
• Review configuration options for client APQ

APQ from the client

We can mimic a client—such as a frontend app running Apollo Client, which supports APQ—using a curl command in the terminal.

Let's build out our command. We'll send a new request to our router on http://127.0.0.1:5000. Next, define a --header flag with a value of 'content-type: application/json'.

We'll also specify two separate instances of --data-urlencode.

Recall that the first time we send the query to the router, we need to send the actual full-length query string AND its identifier (its SHA-256 hash).

Let's use the first --data-urlencode flag to pass in our entire query string. We include it in the following format:

To include the hash as part of the second --data-urlencode flag, we'll define a lengthier string with some additional data. We start by specifying extensions, and set it equal to an object with a persistedQuery key. As the value for persistedQuery, we'll define another object.

This next object takes two keys: version and sha256hash. We've pre-calculated the SHA-256 hash of the provided query, so you can copy the contents below.

Here's what the entire command should look like. Pop open a terminal, and let's run it!

After just a moment, we'll see the response with our data!

Now let's try it again; this time removing the full query string from our curl command.

With this command, we can send just the operation identifier, and our router knows exactly which operation we're talking about. We should see the exact same response in the terminal as before.

Caching client operation APQ

The router enables caching client operation APQ by default. We can further customize how many operations it stores, or even turn off the feature entirely, by setting some flags in our router-config.yml file.

We can also cache our APQ in a distributed cache, which we'll see later on in the course.

Practice

Key takeaways

• To support sending the router APQ, a client should implement the logic to convert operation strings to hashes, to send the router these hashes, and to retry the request in the event the router requires the original query string. Apollo Client supports APQ out of the box.

Up next

Receiving queries from clients isn't the router's only job; it must also divide queries between the subgraphs responsible for providing data. In the next lesson, we'll walk through how the router takes on the role of client when sending APQ to subgraphs.