api.md

Origin API

Creating a new Origin connector.

To create a new Origin, you should extend from the Mercury Origin Class, defining the behavior of the methods _create, _read, _update and _delete.

If you don't define one of this methods, the correspondant CRUD method will not be available in the resultant Origin.

Call super from your own constructor, passing:

• super([id, defaultValue, options])
  • Arguments:
    • defaultId - <String> Used for debugging purposes. The _id of the resultant source will be a hash calculated using this default id and default value (only in case it is not a callback).
    • defaultValue - <Any> Resultant origin will have this value in the value property until data is fetched. If a <Function> is provided, it will be executed to obtain the default value, passing the current query as argument.
    • options - <Object> Object containing another options, such as:
      • uuid - <String> If provided, the resultant instance will have this property as _id. It will not be "hashed".
      • tags - <String> or <Array of Strings> Tags to be assigned to the instance when created. Tags are used by "sources" handler. For further info read the sources documentation.

Crud methods will receive two arguments:

• _read([query, extraParams])
  • Arguments:
    • query If origin is queried, you will receive here the current query.
    • extraParams Extra data passed as argument when the method is invoked.
  • Returns: <Promise>

Available methods for internal usage:

• this._cache Use built-in cache to provide cache to your Origin.
  • this._cache.set(query, value). Set cache for an specific query. Cached objects should be Promises, in order to provide cache too for parallel invokations.
  • this._cache.get(query). Returns cache for an specific query.
  • this._cache.clean([query]). Clean cache of an specific query. Cleans all caches if no query is provided.

Example

import { Origin } from "@xbyorange/mercury";
import requestPromise from "request-promise";

export class Request extends Origin {
  constructor(url, options = {}) {
    super(url, options.defaultValue, options.uuid);
    this._url = url;
  }

  _read(query) {
    const cached = this._cache.get(query);
    if (cached) {
      return cached;
    }
    const request = requestPromise({
      uri: this._url
    }).catch(err => {
      this._cache.set(query, null);
      return Promise.reject(err);
    });
    this._cache.set(query, request);
    return request;
  }
}