Page 1 of 1
Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 12:03
by Wilop91
Hello
I wrote a simple program that has 2 timers and 2 callbacks.
Each timer launches a database query (one to select Temperature and one to select KWH) with a callback
Code: Select all
if (MyMinute == MyMinute2Run ) then --Get Temperature data
--Prepare CMD with SELECT-FROM-WHERE
dz.executeShellCommand( { command = cmd, callback = 'myTMPcallback', })
end
Each callback processes the data and stores it in tables (one for Temperature and one for KWH)
I defined those tables as "global" in the "data" section
Code: Select all
data = {global_myKWHTable = { initial={} }, global_myTMPTable = { initial={} },},
I re-assigned a specific name to the tables at the start of the program
Code: Select all
execute = function(dz, triggeredItem, triggerInfo)
myKWHTable = dz.data.global_myKWHTable
myTMPTable = dz.data.global_myTMPTable
And I initialized the tables in each callback
Code: Select all
if (triggeredItem.statusCode == 0) and (triggerInfo.trigger == "myTMPcallback") then
myTMPTable={}
myTMPTable[1]={}
myTMPTable[2]={}
local myPayload = triggeredItem.data
--Format of received data: 4|TempHumBaro|10.80|2026-03-05
--I store the data in myTMPTable table - index [1] holds Temperature and index [2] holds dates
--I can print out the contents of the myTMPTable table
end
And I do the same in the KWH callback
Since both tables are global I thought I would be able to use its contents everywhere in my program. But that's not the case. Those tables seems to be "local" to each callback.
What I'm doing wrong here?
In advance many thanks for your help
Willy
Re: Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 16:44
by RonkA
Is there somewhere in your script where you take your new received data and fill the global data with it?
Re: Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 17:20
by willemd
A bit confusing to use the term global while you actually define the persistent variables as "script level" persistent variables (see wiki). Global persistent variables can be defined in dzVents to use between different scripts but that is not the case here and you don't define them as such, so the naming is confusing.
But even at script level you should be able to use the variables between different runs of the script. That is the whole point of persistent variables.
I think it might have to do (but I am just guessing) with your re-assignment to a different name. Maybe this is creating a copy of the persistent data. You then initialize and add contents to the copy, but not to the persistent variables themselves. I would rewrite the script just using the names of the persistent data and test whether it makes a difference.
Re: Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 17:37
by Wilop91
Hi RonkA
Thanks for your reply
RonkA wrote: Sunday 08 March 2026 16:44
Is there somewhere in your script where you take your new received data and fill the global data with it?
I populate the tables within each callback (myTMPcallback and myKWHcallback) with the data i got from the SQL queries.
I get this error:
Code: Select all
attempt to concatenate a nil value (field '?')
I concluded my tables are "local" to each callback routine and not "global" as expected.
My SQL queries work as expected and in each callback I get the data I see in Domoticz database. As a result I can printout the contents of the table which within each callback.
But I cannot printout the other global table.
This is an extract of my program - sorry I'm not a good programmer:
Code: Select all
local MyHour2Run = "10"
local MyMinute2Run = "53" --01
local MyMinute2Stop = "54" --25
local debugLinky = false
return {
on = { timer = { 'every minute between ' .. MyHour2Run .. ':' .. MyMinute2Run .. ' and ' .. MyHour2Run .. ':' .. MyMinute2Stop },
shellCommandResponses = {'myTMPcallback','myKWHcallback', } },
data = {global_myKWHTable = { initial={} }, global_myTMPTable = { initial={} },},
logging = {level = domoticz.LOG_INFO, marker = 'CalculateAverages',},
execute = function(dz, triggeredItem, triggerInfo)
myKWHTable = dz.data.global_myKWHTable
myTMPTable = dz.data.global_myTMPTable
if triggeredItem.isTimer then
MyMinute = os.date("%M")
if (MyMinute == MyMinute2Run ) then --Get Temperature data
--Prepare CMD with SELECT-FROM-WHERE
dz.executeShellCommand( { command = cmd, callback = 'myTMPcallback', })
end
if (MyMinute == MyMinute2Stop ) then --Get KWH data
--Prepare CMD with SELECT-FROM-WHERE
dz.executeShellCommand( { command = cmd, callback = 'myKWHcallback', })
end
elseif triggeredItem.isShellCommandResponse then
dz.log("Received ShellCommandResponse callback = " .. triggerInfo.trigger, dz.LOG_INFO)
if (triggeredItem.statusCode == 0) and (triggerInfo.trigger == "myTMPcallback") then
dz.log("Received TMP callback is OK", dz.LOG_INFO)
myTMPTable={}
myTMPTable[1]={}
myTMPTable[2]={}
local myPayload = triggeredItem.data
--Format of received data: 4|TempHumBaro|10.80|2026-03-05
--I store the data in myTMPTable table - index [1] holds Temperature and index [2] holds dates
--I can print the contents of myTMPTable table
end
if (triggeredItem.statusCode == 0) and (triggerInfo.trigger == "myKWHcallback") then
dz.log("Received KWH callback is OK", dz.LOG_INFO)
myKWHTable={}
myKWHTable[1]={}
myKWHTable[2]={}
local myPayload = triggeredItem.data
--Format of received data: 13|KWH|14843|2020-11-17
--I store the data in myKWHTable table - index [1] holds KWH and index [2] holds dates
--I can print the contents of myKWHTable table
--
--But I cannot print myTMPTable which is supposed to be a global table
end
end
end
}
Re: Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 17:42
by Wilop91
Hi Willemd
willemd wrote: Sunday 08 March 2026 17:20
A bit confusing to use the term global while you actually define the persistent variables as "script level" persistent variables (see wiki). Global persistent variables can be defined in dzVents to use between different scripts but that is not the case here and you don't define them as such, so the naming is confusing.
But even at script level you should be able to use the variables between different runs of the script. That is the whole point of persistent variables.
I think it might have to do (but I am just guessing) with your re-assignment to a different name. Maybe this is creating a copy of the persistent data. You then initialize and add contents to the copy, but not to the persistent variables themselves. I would rewrite the script just using the names of the persistent data and test whether it makes a difference.
You are right - I should rather use "persistent". I made the "re-assignment" to make reading of the program easier.
I will give this a try and revert back later
Thanks
Willy
Re: Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 18:08
by RonkA
i am not a programmer! but in my logic you state:
But I cannot printout the other global table.
I Don't see anywhere in your script the table is actually written into the persistent variable.. (like to dz.data.global_myKWHTable)
So there is nothing to be printed there.
Re: Need help to understand the use of global persistant data...
Posted: Sunday 08 March 2026 19:33
by Wilop91
Hello RonkA and Willemd
Thanks for your replies
Using everywhere in my program dz.data.global_myTMPTable and dz.data.global_myKWHTable to access the tables makes them persistent.
I will try to make the table names a bit shorter to make my program more readable
Best regards
Willy