I also wanted to understand why GQL was getting so much attention in a REST vs GraphQL way so I implemented a GQL microservice that had the same features as a service that I had implemented previously as REST. Both services ran on node.js and connected to the same data stores, etc. I ran both services on the same load test lab and documented my findings at https://glennengstrand.info/software/architecture/microservi...
The TL;DR of that blog is this. There isn't much value that GQL can provide over REST + OpenAPI. GQL is still in its infancy so APM is easier with REST. The biggest argument for GQL is returning the right amount of data but GQL is slightly slower than REST because the server is having to parse what is essentially a mini program with every request.
If you're a front end developer the advantages a clear because of much superior tooling. The reason for this the agreed SDL spec format which is part and parcel of GQL. REST is just a loose collection of ideas and OpenAPI is not integral to REST as theres no single over arching spec of organisation for REST.
In my experence therefore, the tooing (code gen, doc gen) etc around OpenAPI is piss poor in comparison to gql. Just look at GraphIQL compared to postman.
The above referenced PoC service based on express uses https://github.com/apigee-127/swagger-tools which surfaces a web app by which front end devs navigate through the published API endpoints. They can use the web app to call the service via the endpoint or copy and paste sample code that calls the service. Most open api integrations support this kind of functionality.
From my experience, front-end developers are the last people that want to learn how to query a complex data model. It's usually much preferable if the backend team exposes the required endpoints for any UI operation, since they have much more fine-grained control on the DB and a much clearer intuition on what is easy to do and what isn't.
The TL;DR of that blog is this. There isn't much value that GQL can provide over REST + OpenAPI. GQL is still in its infancy so APM is easier with REST. The biggest argument for GQL is returning the right amount of data but GQL is slightly slower than REST because the server is having to parse what is essentially a mini program with every request.