hmincrby.lua

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-- Multi HINCRBY via a LUA script
-- Increments a list of fields in a hash stored at key.
-- KEYS : key of the hash 
-- ARGS : list of field/increment
-- Note : Because a script is executed in an atomic way, you should always use this script to increment fields values.
-- ex via cli : redis-cli --eval hmincr.lua myhash , 1 10 2 20
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-- gets multiple fields from a redis hash as a dictionary
local hmget = function (key, args)
	if next(args) == nil then return {} end
	local bulk = redis.call('HMGET', key, unpack(args))
	local result = {}
	for i, v in ipairs(bulk) do result[args[i]] = v end
	return result
end

-- sets all fields for a redis hash from a dictionary 
local hmset = function (key, dict)
  if next(dict) == nil then return nil end
	local bulk = {}
	for k, v in pairs(dict) do
		table.insert(bulk, k)
		table.insert(bulk, v)
	end
	return redis.call('HMSET', key, unpack(bulk))
end

-- script
local fields = {}
local fieldsAndValues = {}

for i=1,#ARGV,2 do
    -- list of hash fields to get
    table.insert(fields, ARGV[i])
    -- dictionary of args
    fieldsAndValues[ARGV[i]] = tonumber(ARGV[i + 1])
end

local hfields = hmget(KEYS[1], fields)

for k, v in pairs(fieldsAndValues) do
    local current = hfields[k]
    -- never returns nil, but it returns a boolean value (false) if no key exists.
    if (current==nil or (type(current) == "boolean" and not current)) then
        -- init fields
        hfields[k]=v
    else
        -- incre
        hfields[k]=v+tonumber(hfields[k])
    end
end

-- update the hash
hmset(KEYS[1], hfields)

return #fields