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Redis

Our system uses Redis to load and cache news and games that are fetched from the internet or the database. The Redis package is defined in com.goodboards.redis which is defined in the redis-interface component.

Quick overview of Redis Use in goodboards

We use two Redis lists, Games and News to push and cache records as needed and use a rpop (right pop) to retrieve elements from the list.

Local Setup

Installation

  1. If you have pip installed you can use pip install redis to install Redis on you computer.
  2. Start redis server by using redis-server in terminal.
  3. Once the server has started, open a new terminal tab and enter redis-cli, enter the command PING and Redis will respond with PONG confirming the server has started.
  4. That's it, installation is complete :D

Environment Variables

  1. The Goodboards app will access redis through a environment (env) variable called REDIS_URL, so for Redis to work properly you will need to set the env variable. On Mac,
    you can use export REDIS_URL=redis://localhost:6379 to confirm the variable has been set use echo $REDIS_URL
  2. And that's it ;D

Redis Package Contents

Main Components

  • RedisInterface - Class for accessing Redis Queue

Utilities

  • SystemWrapper - Contains utility functions to access env variables.

Class Methods & Properties

Properties

// Get REDIS_URL env variable value   
private val redisHost = SystemWrapper.getenv("REDIS_URL")
// Create a redis client for the given host url
private val redisClient: RedisClient = RedisClient.create(redisHost)
// Connect the client to redis server at the host url, creating a connection
private val connection: StatefulRedisConnection<String, String> = redisClient.connect()
// connection.sync returns a RedisCommands instance that us to synchronously execute Redis command over the connection
private val redisCommands: RedisCommands<String, String> = connection.sync()

Methods

fun pushToList(name: String, values: List<String> {
    redisCommands.lpush(name, *values.toTypedArray())
}

This function takes two arguments, a name and a list of string. Then it converts this list of strings to an array of strings, spreads it using the * spread-operator pushes all the strings to the start or left the list named 'name' on the Redis server. If the there is no list with that name then a new list is created with that name.

fun getFromList(name: String, count: Long = 1): List<String> {
    return redisCommands.rpop(name, count)
}

This method takes two arguments name (name of the list) and count (number of elements to get from the right side of the list). The default value of count is set to 1.

fun close() {
    connection.close()
    redisClient.shutdown()
}

This method is used to close the Redis connection and shutdown the Redis client. It does not take any parameters.

Example

import com.goodboards.redis.*
val redisInterface = RedisInterface()
redisInterface.pushToList("Games", listOf<String>("{name: 'Chess', desc:'Good Game'}"))
println(redisInterface.rpop("Games"))
// prints -> "{name: 'Chess', desc:'Good Game'}"