Deleting multiple keys in redis-rb

For a Rails app I'm working on, I needed to test the results of loading and unloading redis data.

The namespace is determined by the environment, avoids interacting with development. This worked well.

def clear_redis_cache
  keys = $redis.keys "#{namespace}*"
  $redis.del(*keys) unless keys.empty?
end

This is better achieved using the enumerator returned by scan_each.

scan_each(match: 'autocomplete_*').each do |key|
  del key
end

This does not load all of the matching keys into memory at once, so it will not be limited by local memory.

A little coding exploration of the way the splat operator works:

def foo(*keys)
  puts keys.inspect
end

>> foo("hi", "there")
["hi", "there"]

>> foo(["hi", "there"])
[["hi", "there"]]

>> foo(*["hi", "there"])
["hi", "there"]

So passing in a regular array will cause that array to be evaluated as a single item, so that you get an array inside an array within your method. If you preface the array with * when you call the method:

$redis.del(*keys)

That lets the method know to unpack it/not to accept any further arguments. So that should solve the problem that you're having!

Just for the sake of further clarification, this works:

>> foo("hello", *["hi", "there"])

This causes a syntax error:

>> foo("hello", *["hi", "there"], "world")