How do I represent this data using Redis? - redis

Question

I want to be able to store data such as "store x is open between 9am and 5pm on Monday but it's only open during 9am and 12pm on Saturday"
What's the best way to store this using redis?
I would later like to query it using something like this. Show me all stores that are open on Saturday at 10:30am

Answer 1

In Redis, like most if not all other NoSQL databases, you want to store your data in the manner that's most suitable for answering the query. There are quite a few ways you can represent this data and answer the query, choosing between them requires knowledge about the other access patterns that you need to support.
However, in the context of this specific question alone, the simplest way of doing that IMO is to use two Sorted Sets per for each day of the week. Assuming that stores are open continuously and at most once each day (i.e. no siestas), the members of these Sorted Sets should be the store ids and the scores their opening hours - the first Sort Set's scores will denote the time that the store opens whereas the second's the time it closes. For example:
ZADD monday:open 9 store:x
ZADD monday:close 17 store:x
ZADD saturday:open 9 store:x
ZADD saturday:close 12 store:x
Once you have all the Sorted Sets in place, answering the query requires two calls to ZRANGEBYSCORE and intersecting the results. The snippet below demonstrates how to do it using Lua since doing using server scripts will be more efficient than moving the entire thing to the client in most cases.
Note: an alternative approach to doing the intersect in Lua is actually storing the temporary results in Redis' Sets and calling SINTER.
-- helper function to make a "set" out of a table
local function makeset(t)
local r = {}
for _, v in ipairs(t) do r[v] = true end
return(r)
end
-- get opening and closing hours for a given day
local ot = redis.call('ZRANGEBYSCORE', KEYS[1], '-inf', ARGV[1])
local ct = redis.call('ZRANGEBYSCORE', KEYS[2], '(' .. ARGV[1], '+inf')
-- convert to sets and choose the smaller set as s1
local s1 = {}
local s2 = {}
if #ot < #ct then
s1 = makeset(ot)
s2 = makeset(ct)
else
s1 = makeset(ct)
s2 = makeset(ot)
end
-- intersect s1 and s2
local t = {}
for k in pairs(s1) do
t[k] = s2[k]
end
-- prepare a response table
local r = {}
for k in pairs(t) do
r[#r+1] = k
end
return(r)
Run this script by passing to it the two keys and the hour, like so:
redis-cli --eval storehours.lua saturday:open saturday:close , 10.5