From REST to GraphQL - Meetup

This is a GraphQL example for the GraphQL meetup in Rome.
We are going to use the reference implementation of GraphQL for JavaScript.

To start the tutorial:

• clone this repository
• git checkout 1.0.1

Data model

This is the data model we would like to define:

+----------------------------------+         +----------------------------+         +---------------------+
| QueryType                        |         | ReservationType            |         | HotelType           |
+----------------------------------+         +----------------------------+         +---------------------+
|                                  |         |                            |         |                     |
| reservations: [ReservationType]! +-------> | reservationNumber: ID!     |         | hotelName: String!  |
|                                  |         | checkIn: String!           |         | fullAddress: String |
+----------------------------------+         | checkOut: String!          |         | starRating: Int!    |
                                             | hotel: HotelType!          +-------> |                     |
                                             | status: ReservationStatus! |         +---------------------+
                                             |                            |
                                             +----------------------------+

GraphQL Schema Definition

Using the GraphQL SDL (i.e. schema definition language), the data model can be described in this way:

• src/schema/reservations.graphqls

Resolvers

Resolvers definition:

• src/schema/resolvers.js

Executable schema

Loading the executable schema:

• src/schema/index.js

Starting the server

This is the recipe:

• src/index.js

...and then start the server with the command: node ./src/index.js

Our first query

First query:

{
  reservations(userId: 4115) {
    reservationNumber,
    checkIn,
    checkOut
  }
}

Try the first query in the browser.

Introspection query

The GraphQL introspection feature is the ability of exposing information about what queries are supported. Example introspection query:

{
  __schema {
    types {
      name,
      description
    }
  }
}

Try the GraphQL the introspection query.

This feature leads to really nice features like:

• Auto documentation: the client knows the exact GraphQL schema.
• Code generation: the client can use a client generated from the schema.
• Static validation: the GraphQL client can validate the query before sending it to the server

GraphiQL

GraphiQL is a Schema Explorer that use the GraphQL introspection feature.

• git checkout 1.0.2
• restart the server and access to GraphiQL

More complex example

Introduce an additional resolver in order to gather hotel data from the HotelService:

• git checkout 1.0.3