joserfjuniorllms / reservatron

Table reservation service.

Reservatron

Reserve table service. Use redis distributed lock to guarantee reliable reservations even when multiple instances of Reservatron are running. This service uses GraphQL API via this library.

Future improvements:

• pagination. Easy way will be integrate querydsl and compose queries in repositories to support pagination on DB level
• filtering. Also querydsl could be used to optimise requests like getAllTables(filter: {tableId: 1})
• unsubscribe subscriptions on connection close (due to the strange bug subscriber's onConnect is not called)
• subscriptions in case of multiple instances. Need to send events with reservations to Kafka and publish updates for subscribed clients.

In docker

Ensure you've built Admin before.

sudo ./gradlew build docker -x test -x test_integration
sudo docker-compose up -d

In OS

export POSTGRES_HOST=localhost
export REDIS_HOST=localhost
./gradlew bootRun

Testing

./gradlew check

Protocol

Graphql is used for communication. Make introspective query to get schema for details. Endpoint for query and mutations is /graphql, for subscriptions is /subscriptions

Examples:

Make a reservation for a table

Method: POST

Body:

mutation ReserveTable
{   reserveTable(input: {tableId: 1,
                         guest: "Test",
                         from: "2018-01-04T18:00:00.000+0000",
                         to: "2018-01-04T19:00:00.000+0000",
                         clientMutationId: "uuid"})
    {status}
}

Response:

{
    "data": {
        "reserveTable": {
            "status": "CONFLICT"
        }
    },
    "errors": [],
    "extensions": null
}

Show all reservations for all tables

Method: POST

Body:

query {allTables
        {edges {node {name reservations
                              {edges {node {guest from to}}}
                     }
               }
        }
      }

Response:

{
    "data": {
        "allTables": {
            "edges": [
                {
                    "node": {
                        "name": "test",
                        "reservations": {
                            "edges": [
                                {
                                    "node": {
                                        "guest": "Test",
                                        "from": "2018-01-04T18:00:00.000+0000",
                                        "to": "2018-01-04T19:00:00.000+0000"
                                    }
                                }
                            ]
                        }
                    }
                },
                {
                    "node": {
                        "name": "test2",
                        "reservations": {
                            "edges": []
                        }
                    }
                }
            ]
        }
    },
    "errors": [],
    "extensions": null
}

Subscribe for table reservations

Websocket

Body:

subscription RealTimeReservationsSubscription {
               newReservationMade(tableId: 1) {
                 guest
                 from
                 to
               }
             }

On every new subscription to this server you will receive a Reservation. Important! This repo is just an example of graphql usage. With multiple instances of this service subscriptions won't work correctly, as one instance doesn't receive events about subscription has been made from the other. Important! Subscriptions unsubscribe feature is not working now. CompletionStageMappingPublisher's onSubscribe is not called, thus link between GraphqlSubscriber and Subscription can't be made. As a result, when connection is closed we can't cancel subscription.