redis hmget with wildcard fields

Question

I have a hashset in redis like below.

"abcd" : {
 "rec.number.984567": "value1",
 "rec.number.973956": "value2",
 "rec.number.990024": "value3",
 "rec.number.910842": "value4",
 "rec.number.910856": "...",
 "other.abcd.efgh": "some value",
 "other.xyza.blah": "some other value"
 "..." : "...",
 "..." : "...",
 "..." : "...",
 "..." : "..."
}

if I call hgetall abcd, it will give me all fields in the hash. My objective is to get only those fields of the hashset that begin with "rec.number". When I call like

 redis-cli hmget "abcd" "rec.number*", 

it gives me a result like

1)

Is there a way to retrieve data for only those keys which start with my expected pattern? I want to retrieve only those keys because my dataset contains many other irrelevant fields.

• tkruse: Possible duplicate of Redis / Get all keys & values from redis with prefix

Answer 1

HMGET do not supports wildcard in field name. You can use HSCAN for that:

HSCAN abcd 0 MATCH rec.number*

More about SCAN function in official docs.

LUA way

This script does it in LUA scripting:

local rawData = redis.call('HGETALL', KEYS[1]);
local ret = {};
for idx = 1, #rawData, 2 do
 if string.match(rawData[idx], ARGV[1]) then
 hashData[rawData[idx]] = rawData[idx + 1];
 end 
end

Nice intro about using redis-cliand LUA in Redis may be found in A Guide for Redis Users.

• Itamar Haber: In the Lua script, you should actually use HSCAN as well. If the Hash is big enough/RAM is tight, this will reduce the Lua engine's heap.