03-dynamic-facts.mts

/*
 * This example demonstrates computing fact values at runtime, and leveraging the 'path' feature
 * to select object properties returned by facts
 *
 * Usage:
 *   node ./examples/03-dynamic-facts.js
 *
 * For detailed output:
 *   DEBUG=json-rules-engine node ./examples/03-dynamic-facts.js
 */

import "colors";
import { Engine } from "json-rules-engine";

// example client for making asynchronous requests to an api, database, etc
import apiClient from "./support/account-api-client.mjs";

async function start() {
  /**
   * Setup a new engine
   */
  const engine = new Engine();

  /**
   * Rule for identifying microsoft employees taking pto on christmas
   *
   * the account-information fact returns:
   *  { company: 'XYZ', status: 'ABC', ptoDaysTaken: ['YYYY-MM-DD', 'YYYY-MM-DD'] }
   */
  const microsoftRule = {
    conditions: {
      all: [
        {
          fact: "account-information",
          operator: "equal",
          value: "microsoft",
          path: "$.company", // access the 'company' property of "account-information"
        },
        {
          fact: "account-information",
          operator: "in",
          value: ["active", "paid-leave"], // 'status'' can be active or paid-leave
          path: "$.status", // access the 'status' property of "account-information"
        },
        {
          fact: "account-information",
          operator: "contains",
          value: "2016-12-25",
          path: "$.ptoDaysTaken", // access the 'ptoDaysTaken' property of "account-information"
        },
      ],
    },
    event: {
      type: "microsoft-christmas-pto",
      params: {
        message: "current microsoft employee taking christmas day off",
      },
    },
  };
  engine.addRule(microsoftRule);

  /**
   * 'account-information' fact executes an api call and retrieves account data, feeding the results
   * into the engine.  The major advantage of this technique is that although there are THREE conditions
   * requiring this data, only ONE api call is made.  This results in much more efficient runtime performance.
   */
  engine.addFact("account-information", async function (_params, almanac) {
    const accountId = await almanac.factValue<string>("accountId");
    return apiClient.getAccountInformation(accountId);
  });

  // define fact(s) known at runtime
  const facts = { accountId: "lincoln" };
  const { events } = await engine.run(facts);

  console.log(
    facts.accountId + " is a " + events.map((event) => event.params!.message),
  );
}
export default start();

/*
 * OUTPUT:
 *
 * loading account information for "lincoln"
 * lincoln is a current microsoft employee taking christmas day off
 *
 * NOTES:
 *
 * - Notice that although all 3 conditions required data from the "account-information" fact,
 *   the account-information api call is executed only ONCE.  This is because fact results are
 *   cached by default, increasing performance and lowering network requests.
 *
 * - See the 'fact' docs on how to disable fact caching
 */