If you’re interested in the details, it’s worth checking out the spec itself, but the most important thing is:
GraphQL is an API.
GraphQL tries to improve the way clients communicate with remote systems. An Application Programming Interface. As such, it’s a direct replacement for REST.
GraphQL doesn’t require any specific technology or language. A GraphQL server can be built in any technology, just like a REST server.
GraphQL’s power comes from a simple idea — instead of defining the structure of responses on the server, the flexibility is given to the client. Each request specifies what fields and relationships it wants to get back, and GraphQL will construct a response tailored for this particular request. The benefit: only one round-trip is needed to fetch all the complex data that might otherwise span multiple REST endpoints, and at the same time only return the data that are actually needed and nothing more.
That is huge. Like moving from SOAP to REST.
Another advantage that I see in GraphQL is that it has a built-in type introspection. That means you can describe the entire API programmatically, and we can build tools that drastically improve development. REST APIs don’t have that — although there are several proposals for a REST API schema, there isn’t one standard that everyone would use. SOAP has WSDL, but it has many problems of its own.
So does it mean REST is over?
The industry has invested a lot in REST APIs, in fact the area is rapidly growing, with many companies opening their APIs to the outside world, and many startups building tools to support the ecosystem.
Currently, the only production use case of GraphQL is at Facebook. It works great for them but we’re still yet to see how it will work for everyone else.
Update 22 Dec 2016: Many companies are now running GraphQL in production, see e.g. https://www.quora.com/Who-is-using-GraphQL-in-production-besides-Facebook-itself
Even if GraphQL was so much better than REST, it would take at least 10 years for the industry to switch. 10 years on the Internet is like a lifetime — heck, we might not even have React anymore.
It’s likely that if GraphQL proves to be effective, it will co-exist with REST APIs. Some APIs will use REST, some will use GraphQL. Some might support both.
GraphQL with REST
Current REST APIs can be exposed to GraphQL clients by building a GraphQL server as a wrapper around the REST API. A client would talk to a GraphQL server which would translate the query to (multiple) REST APIs. Client only sends one request, and receives the smallest possible response it needs. The server has much better bandwidth so the extra queries are not so critical.
Relay is a GraphQL client library for React. It has pluggable transport layer that abstracts fetching data from a GraphQL server. The “server” doesn’t have to be running remotely though; it could be packaged as part of the client app itself.
You can imagine building a library that would create a GraphQL spec out of a REST API; let’s call it graphql-rest. You could implement it as a transport layer for Relay. Relay would manage the local state, handle optimistic updates and many other amazing things, and graphql-rest would translate the queries to REST calls.
At the same time, graphql-rest could be used as a GraphQL server, too. Without changing a line of code, the developer could then choose whether they want to optimize for data transport (and run graphql-rest as a server that the client app talks to), or have a simpler architecture (bundle graphql-rest with the app and run it on the client).
Discuss on HN: https://news.ycombinator.com/item?id=9847758
Thanks to @en_js for providing insights into how Relay works.
Update 5 Nov 2016: Okay, graphql-rest is dead as I have switched jobs and this project is not a priority right now. However, there have been some developments of this concept if you’d like to check them out: