Redis: Expand key references in values to their values - lua

Question

I am fairly new to redis. I have a CMS that outputs JSON to redis in a structure like this:
partial:1 => {id: 1, title: 'Foo1', ...}
partial:2 => {id: 2, title: 'Foo2', ...}
partial:3 => {id: 3, title: 'Foo3', ...}
page:home => {
id: 'Homepage',
teaser1: 'partial:1',
teaser2: 'partial:2',
teaser3: {type: Slider, content: 'partial:3'}
}
So the JSON can contain other redis-keys that conform to a certain naming scheme in its structure. What I would like to have is a way to query redis so that when I get the page:home-key the references to other keys in the json get 'expanded' to their respective values, like this:
{
id: 'Homepage',
teaser1: {id: 1, title: 'Foo1', ...},
teaser2: {id: 2, title: 'Foo2', ...},
teaser3: {type: Slider, content: {id: 3, title: 'Foo3', ...}
}
Is this possible and how could it be achieved?

Answer 1

Yes. it is quite possible. Here's a working approach:
Create a function to convert your redis hashes (e.g: partial:*,page:home) to lua tables: hgetall
Create a function to check if the given redis hashname conforms with your naming scheme, if so use hgetall to convert it to a lua table; otherwise return the same value: evaluate_hash
Create a function to evaluate and convert all properties of a given hash name and return it as a json: expand
Here's a simple implementation:
--Script: redis_expand_as_json.lua
--Function to Convert a given hash name (e.g: partial:1..n, page:home) to a lua table
local function hgetall(a)local b=redis.call('HGETALL',a)local c={}local d;for e,f in ipairs(b)do if e%2==1 then d=f else c[d]=f end end;return c end
--Function to check if the given value conforms with a naming scheme,
-- if so convert it to a lua table; otherwise return the values as is.
local function evaluate_hash(value)
local pattern = "partial:%d+"
if string.match(value, pattern) then
return hgetall(value)
else
return value
end
end
--Function to convert a given hash_name to a lua table,
-- iterate all elements and convert them to lua table if necessary
-- returns the table as a json object
local function expand(hash_name)
local obj_table = hgetall(hash_name)
for k, val in pairs(obj_table) do
obj_table[k] = evaluate_hash(val)
end
return cjson.encode(obj_table)
end
local page = KEYS[1]
local json_result = expand(page) or {}
redis.log(redis.LOG_NOTICE, tostring(json_result))
return json_result
Testing in console:
redis-cli -c hmset "partial:1" id 1 title foo1
OK
redis-cli -c hmset "partial:2" id 2 title foo2
OK
redis-cli -c hmset 'page:home' id 'Homepage' teaser1 'partial:1' teaser2 'partial:2'
OK
redis-cli EVAL "$(cat redis_expand_as_json.lua)" 1 'page:home'
{"teaser1":{"id":"1","title":"foo1"},"teaser2":{"id":"2","title":"foo2"},"id":"Homepage"}

Answer 2

I don't know Redis but perhaps this works for you:
local T=[[
partial:1 => {id: 1, title: 'Foo1', ...}
partial:2 => {id: 2, title: 'Foo2', ...}
partial:3 => {id: 3, title: 'Foo3', ...}
page:home => {
id: 'Homepage',
teaser1: 'partial:1',
teaser2: 'partial:2',
teaser3: {type: Slider, content: 'partial:3'}
}
]]
local D={}
for k,v in T:gmatch("(%w+:%w+)%s*=>%s*(%b{})") do
D[k]=v
end
print((T:gsub("'(.-)'",D)))