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Overview
Elide support for GraphQL subscriptions would allow interactive websockets and also eliminate client-side polling large models for changes. The proposed subscriptions would notify clients of any changes (create, delete, update) to any Elide model in realtime.
Annotations
The elide-graphql package will support the following new model annotation:
Models or their properties can be annotated. If only the model is annotated, it signifies that all fields within the model are available for subscription. If individual fields within a model are annotated, only those fields, are available for subscription. (It is important to limit the field set available for subscriptions to minimize unnecessary data published to subscription topics. )
GraphQL Schema
A
Bookmodel annotated with theSubscriptionannotation would produce a GraphQL schema as follows:The
Booktype returned here comes from a separate GraphQL schema for subscriptions. It only includes the attributes and relationships ofBookthat have been annotated as part of the subscription.Subscription Filters
All subscriptions can be filtered by providing a RSQL filter. It is only valid to filter on fields in the subscription annotation.
API Endpiont
Elide graphql will include a new websocket servlet endpoint that exposes subscriptions and their associated schemas.
Pub/Sub Configuration
Elide will leverage JMS to communicate with a pubsub message bus to:
Subscriptionannotation.Implementation Details
The following is a brief synopsis of how this feature might be implemented.
GraphQL-Java Version
An upgrade to the latest GraphQL-java version should not be required to implement this RFC.
Two Elide Instances
Subscriptions will leverage a different
Elideinstance backed by a new read-onlyDataStorethat can read from JMS topics. The DataStore will manage all models that include theSubscriptionannotation. The new DataStore will leverage Elide's dynamic type system to create new data types for Elide models - limiting the models, attributes, and relationships to only those annotated withSubscription.Lifecycle Hooks
The primary (non-subscription) elide instance will register life cycle hooks for create, update, and delete for any model marked with a
Subscriptionannotation. The lifecycle hook will serialize the impacted object using a custom Jackson serializer and post the resulting JSON to the corresponding topic in JMS.Jackson
A custom Jackson serializer will serialize objects and ignore any attribute or relationship that has not been marked with the
Subscriptionannotation.Custom Data Store
A new, read-only JMSDataStore will be created that:
Subscription.Subscriptionannotation.loadRecordsfunction.MessageListener.Subclass ModelBuilder
A subclass of the GraphQL
ModelBuilderthat builds subscription types instead of mutations & queries.Modified QueryRunner
Modify or subclass the GraphQL
QueryRunnerto support reactive ExecutionResults.New Reactive DataFetcher
A new, simplified, reactive GraphQL
DataFetcherfor subscriptions. Given that pagination will not be supported, we can remove the concept of Nodes and Edges from the response payloads.GraphQL Websocket Servlet
A new servlet that will use the modified
QueryRunnerto execute GraphQL queries and pass the Reactive result to the websocket.Beta Was this translation helpful? Give feedback.
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