programmability.md

Programmability

Redis provides a programming interface allowing code execution on the redis server.

Functions

The following example retrieves a key in redis, returning the value of the key, incremented by an integer. For example, if your key foo has the value 17 and we run add('foo', 25), it returns the answer to Life, the Universe and Everything.

#!lua name=library

redis.register_function {
  function_name = 'add',
  callback = function(keys, args) return redis.call('GET', keys[1]) + args[1] end,
  flags = { 'no-writes' }
}

Here is the same example, but in a format that can be pasted into the redis-cli.

FUNCTION LOAD "#!lua name=library\nredis.register_function{function_name='add', callback=function(keys, args) return redis.call('GET', keys[1])+args[1] end, flags={'no-writes'}}"

Load the prior redis function on the redis server before running the example below.

import { createClient } from 'redis';

const client = createClient({
  functions: {
    library: {
      add: {
        NUMBER_OF_KEYS: 1,
        FIRST_KEY_INDEX: 1,
        transformArguments(key: string, toAdd: number): Array<string> {
          return [key, toAdd.toString()];
        },
        transformReply: undefined as unknown as () => NumberReply
      }
    }
  }
});

await client.connect();

await client.set('key', '1');
await client.library.add('key', 2); // 3

Lua Scripts

The following is an end-to-end example of the prior concept.

import { createClient, defineScript, NumberReply } from 'redis';

const client = createClient({
  scripts: {
    add: defineScript({
      SCRIPT: 'return redis.call("GET", KEYS[1]) + ARGV[1];',
      NUMBER_OF_KEYS: 1,
      FIRST_KEY_INDEX: 1,
      transformArguments(key: string, toAdd: number): Array<string> {
        return [key, toAdd.toString()];
      },
      transformReply: undefined as unknown as () => NumberReply
    })
  }
});

await client.connect();

await client.set('key', '1');
await client.add('key', 2); // 3