Cache

The cache subsystem is designed to store some values for quick access and a unified interface. It is useful when you have some values grabbed from an external API or some stuff that requires a lot of calculation and does not change from time to time.

Caches have an expiration time, and the developer should not worry about checking it. If a value has expired or does not exist, a callback will be executed, and its return value will be used as the value to store in the cache.

note

The cache subsystem handles all values and takes care of serialization/deserialization.

API

The API is simple:

  async getSetValue(
    key: string,
    onNotFound: () => Promise<any>,
    storeTime: number, // in seconds
  ): Promise<any>;

By default, the store time is 5 minutes.

Example:

const cacheTime = 60 * 5; // seconds
const someValueFromCache = await this.app.cache.getSetValue(
  "someKey",
  async () => {
    const someValue = await someLongAsyncOperation();
    return someValue;
  },
  cacheTime // in seconds
);

note

You can request the same value multiple times, and only one callback will be executed. All other calls will be resolved as a Promise (the same promise).

const promiseArr = [];
for (let n = 0; n < 100; n++) {
  promiseArr.push(
    this.app.cache.getSetValue(
      "someKey",
      async () => {
        // Will be called once! Other calls will find that "someKey" is already processing and return the same Promise.
        const someValue = await someLongAsyncOperation();
        return someValue;
      },
      3600
    )
  );
}

Please note that it works that way per process, as checking promises happens at the process level and is not synchronized via a master process.

Configuration

For now, the cache subsystem has no configuration. But please follow the Redis configuration, as the cache depends on it.