Using an array/table with luup.variable_get

Developer's Corner
#1

Not sure what i’m doing wrong, as I’ve tried things a number of different ways - but please could someone have a look at the following and let me know why I’m not returning the values when using a table to populate the luup.variable_get information ? (See below)

local mytable = {	
		{"urn:upnp-org:serviceId:TemperatureSensor1","CurrentTemperature",44},
		{"urn:micasaverde-com:serviceId:LightSensor1","CurrentLevel",45} 
	     }

--confirm the variable_get requests work..
local temp = luup.variable_get("urn:upnp-org:serviceId:TemperatureSensor1","CurrentTemperature",44)
local light = luup.variable_get("urn:micasaverde-com:serviceId:LightSensor1","CurrentLevel",45)
print("temp = ", temp)
print("light = ", light)
print("")

--now use the table to construct the variable_get request--
for k, v in pairs( mytable ) do
	local value1 = luup.variable_get('"'..v[1]..'","'..v[2]..'",'..v[3])
	print(value1)
	local value2 = luup.variable_get(v[1]..','..v[2]..','..v[3])
	print(value2)
end

I’m sure it’s something obvious but I’m just not seeing it…

#2

There is no need for the quotes as the table values are strings and integers.

for k,v in pairs( mytable ) do
	local value1 = luup.variable_get(v[1],v[2],v[3])
	print(value1)
#3

More neatly, you could, of course, do

local value1 = luup.variable_get(unpack(v))

…there’s really no substitute for learning Lua properly.

#4

Many thanks all,

That’s very interesting as I had actually started off with the following that didn’t work…

for k, v in pairs( mytable ) do
	local value0 = v[1],v[2],v[3]
	local value0a = luup.variable_get(value0)
	print("value0a = ", value0a)
end

Please could you help me understand why the above did not return anything,

Agreed, and I’m continually learning, doing the best I can, with the time I have available…

#5

Two points of interest, here.

Multiple assignments:

You know that you can say:

local a = 1
local b = 2

You perhaps know that you can equivalently write:

local a,b = 1, 2

So

local value0 = v[1],v[2],v[3]

only assigns to one variable, so it is the same as:

local value0 = v[1]

Variadic parameters:

Functions can, of course, take different parameter lists. They don’t try to enforce number, or type, of parameters. This call

	local value0a = luup.variable_get(value0)

has only one parameter, since value0 is just a single variable

this call, however,

local value1 = luup.variable_get(unpack(v))

has as many parameters as v has elements, since the function unpack returns all the elements of v as separate parameters.

#6

Thanks @akbooer, now that you put it that way, it makes perfect sense - I don’t know why I didn’t get that, I was scratching my head why only the first one was returned (I think pulling from an array/table threw me)

Quick question regarding this…

I assume the above pulls each ‘v’ in order, so in this case, if the table rows were ordered in another way it wouldn’t work.

#7

Oh yes, of course. Details matter.

If only Vera / MiOS had defined the Luup functions with named parameters, then we could have written:

luup.variable_get {
  device = 42,
  serviceID = “...whatever...”,
  variable = “variable_name_xxx”}

…in any order. But they didn’t, so we can’t.