Spike: KeyValue repository

[bajtos]

Timeboxed to 3 days

See #1447

So far, LB4 persistence story is all about CRUD. Key-value stores are another common scenario we should support. LoopBack 3.x introduced KeyValue API and Redis + eXtremeScale connectors. For LoopBack 4, we need to add Repository implementations for KeyValue API and verify that all pieces work together as expected.

• Add necessary Repository APIs and implementations
• Verify the use case against real Redis instance
• Documentation, example app, blog post

LB 3.x resources for reference:

• http://apidocs.loopback.io/loopback/#keyvaluemodel
• https://github.com/strongloop/loopback-example-kv-connectors
• https://github.com/strongloop/loopback-connector-kv-redis

Proposed repository API:

interface KeyFilter {
  match: string;
};

interface KeyValueRepository<T> {
  get(key: string, options?: object): Promise<T>;
  set(key: string, value: T, options: object & {ttl?: number}): Promise<void>;
  expire(key: string, ttl: number, options?: object): Promise<void>;
  ttl(key: string, options?: object): Promise<number>; // find a better name than ttl?

  iterateKeys(filter: KeyFilter, options?: object): AsyncIterator<T>;
  keys(filter: KeyFilter, options?: object): Promise<T[]>;
}

Acceptance criteria

• Write a throw-away spike to find out how much work is needed to provide KeyValueRepository as an addition to EntityCrudRepository. Discuss the proposed implementation in a pull request, get it approved at least by @raymondfeng and @bajtos Raymond went ahead and opened a pull request providing a full implementation - see feat(repository): add KVRepository impl using legacy juggler #1539
• Identify follow-up stories that are needed to make this functionality happen. Get the list approved before creating actual GitHub issues
• Create a list of GitHub issues, make sure to include acceptance criteria in each one. Issues should be assigned to "Core-GA" release and Epic [Epic] KeyValue repository #1447.

[jannyHou]

timebox to 3 days.

[bajtos]

@raymondfeng your pull request #1539 is a great step towards a working KeyValue implementation. However, the pull request addresses only the runtime part. IMO, to make this feature easy to use, we need to consider the rest of the story too:

• documentation on loopback.io
• support in boot (if needed?)
• support in CLI
• etc.

[raymondfeng]

Adding docs - #1654

We'll handle the boot/CLI as part of lb4 repository (#1588)

[raymondfeng]

I'm closing this spike as no other github issues need to be opened.