Decode and Parse JSON to Lua - json

Question

I have following JSON data I would like to decode to Lua to access each the publish_topic and sample_rate value.
{"00-06-77-2f-37-94":{"publish_topic":"/stations/test","sample_rate":5000}}
If I understand correctly the Lua table will look like this:
{00-06-77-2f-37-94 = "publish_topic":"/stations/test","sample_rate":5000}
Next I would go through the table to save each value into a local variable.
However, if I try printing out the values of the table (using following code), I get 'nil' as return. Is the code for reading table values wrong?
Does the table have two values or is it just the one: ["publish_topic":"/stations/test","sample_rate":5000] ?
lua_value = JSON:decode(data)
for _,d in pairs(lua_value) do
print(lua_value[d])
end
local topic = lua_value[0]
local timer = lua_value[1]
end
Edit: I am using following JSON library for Lua: http://regex.info/blog/lua/json
Edit2: #Piglet: I implemented your script and modified it by adding a table (conversionTable) in which both elements "publish_topic":"/stations/test" and "sample_rate:5000" would be respectively saved in the variables pubtop and rate. When I however print each of both variables, nil ist returned in both cases.
How can I extract the information out of this table to save in variables?
Ultimately I actually only would like to save the values "/stations/test" and "5000" into these variables. Would I need to parse each of the elements above to get these or is there another way?
local pubtop
local rate
local function printTable(t)
local conversionTable = {}
for k,v in pairs(t) do
if type(v) == "table" then
conversionTable [k] = string.format("%q: {", k)
printTable(v)
print("}")
else
print(string.format("%q:", k) .. v .. ",")
end
end
pubtop = conversionTable[0]
rate = conversionTable[1]
end
local lua_value
local function handleOnReceive(topic, data, _, _)
print("handleOnReceive: topic '" .. topic .. "' message '" .. data .. "'")
-- This sample publishes the received messages to test/topic2
print(data)
lua_value = JSON:decode(data)
printTable(lua_value)
print(pubtop)
print(rate)
end
client:register('OnReceive', handleOnReceive)

Answer 1

I don't know which json library you're using so I can't tell you wether JSON:decode(data) is the correct way.
Assuming lua_value would like like so:
local lua_value = {
["00-06-77-2f-37-94"] = {
publish_topic = "/stations/test",
sample_rate = 5000
}
}
Then your loop
for _,d in pairs(lua_value) do
print(lua_value[d])
end
will indeed print nil.
lua_value has a single element at key "00-06-77-2f-37-94" which is a table.
Each loop iteration will give you a key value pair. So d is actually the value and hence the inner table of lua_value
So you're actually doing this:
local innerTable = lua_value["00-06-77-2f-37-94"]
print(lua_value[innerTable])
Of course lua_value[innerTable] is nil.
Edit:
Try something like
function printTable(t)
for k,v in pairs(t) do
if type(v) == "table" then
print(string.format("%q: {", k))
printTable(v)
print("}")
else
print(string.format("%q:", k) .. v .. ",")
end
end
end
printTable(lua_value)