How do you use lua in redis to return usable result to nodejs - node.js

Question

one of the module i am implementing for my mobile app api is to get all outstanding notifications from , submitting username.
i used a list called username:notifications to store all outstanding id of notifications.
For example, in my test case, ['9','10',11'] is the result after calling for
lrange username:notifications 0 -1
So i wrote a lua script to get lrange and for each result,
hgetall notification:id
And for some reason, lua could not send the table, result to nodejs in usable state. Wondering if anyone
has a solution for multiple hgetall requests and returning them to nodejs
Here goes the rest of the code:
-- #KEYS: "username"
-- #ARGV: username
-- gets all fields from a hash as a dictionary
local hgetall = function (key)
local bulk = redis.call('HGETALL', key)
local result = {}
local nextkey
for i, v in ipairs(bulk) do
if i % 2 == 1 then
nextkey = v
else
result[nextkey] = v
end
end
end
local result = {}
local fields = redis.call('LRANGE' , ARGV[1], 0,-1)
for i, field in ipairs(fields) do
result[field] = hgetall('notification:'..field)
end
return result

Answer 1

You cannot return a "dictionary" from a Lua script, it is not a valid Redis type (see here).
What you can do is something like this:
local result = {}
local fields = redis.call('LRANGE' , ARGV[1], 0, -1)
for i=1,#fields do
local t = hgetall('notification:' .. fields[i])
result[#result+1] = fields[i]
result[#result+1] = #t/2
for j=1,#t do
result[#result+1] = t[j]
end
end
return result
The result is a simple list with this format:
[ field_1, nb_pairs_1, pairs..., field_2, nb_pairs_2, ... ]
You will need to decode it in your Node program.
EDIT: there is another solution, probably simpler in your case: encode the result in JSON and return it as a string.
Just replace the last line of your code by:
return cjson.encode(result)
and decode from JSON in your Node code.