Hi, Am new here, have had a search but forgive me if this has been asked before but could not find the answer. Have installed NodeRed on a Pi that will be receiving data from a GPIO connected RF hat device, the data comes in on the serial port is processed and then makes updates to a MySQL databas…

If you mean by flow variable, message properties, then they exist in the nodes they pass through and new calls to that flow have separate message variables. But are you meaning flow context variable, which exist for any flow in the tab and can cause concurrency issues.

[image] WDL: Have installed NodeRed on a Pi that will be receiving data from a GPIO connected RF hat device, the data comes in on the serial port is processed and then makes updates to a MySQL database installed locally. The data from the serial port is broken down and stored in flow variables a…

Hi E1cid, Thanks for the reply. I receive a CSV string on the MQTT, the message is broken down and assigned to flow.set variables so that they are accessible throughout the flow and various processing performed on them. IF two flows can exist at the same time, are these variable values in scope a…

Node-red is single threaded, so only one node is being processed at any instant. However if a node is waiting for some external process eg updating a database, Node-red is likely to use the time to process another node. As @Colin says, it is a mistake to copy message properties into context variab…

Thanks Colin, just picking up a NodeRed project from someone else, so a new concept and also not that familiar to js, but have found the transition on the language front easy enough. Am impressed in how it works on both Pi and web sever as been easy to implement, just trying to understand and mitig…

Thanks jbudd, Will go through all the replies in a little more detail tomorrow, many thanks for your reply.

Hi, I should have done this originally, this is what I have been doing with the data packet when it first arrives; var oData = msg.payload.split(","); flow.set("Header", oData[0]); flow.set("Type", oData[1]); flow.set("Instruction", oData[2]); flow.set("Index", oData[3]); flow.set("Parameter", oDa…

Yes, much better (and safer). Much more akin to a PURE approach. Context (flow/global) can be useful but they should most definitely not be the goto/first option. When and where context is right/sensible will come with time.

Just to add: There are some nodes that do not respect this approach (i.e. they return a new/blank msg). I always recommend you notify the node author of this and/or move to an alternative node package. As always, the very helpful folk on this forum can advise you when you hit one of these issues.

[image] WDL: IF two flows can exist at the same time, are these variable values in scope across the flows, so if they are changed in one, are they changed across all live instances. Just to clarify, if you are talking about Flows and not processes in a Flow then no, flow context is only 'in s…

Handling variables through the flow

General

Buckskin 6 March 2025 17:35 11

Just to clarify, if you are talking about Flows and not processes in a Flow then no, flow context is only 'in scope' to one Flow so other Flows, even if identical, will not be affected.

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Handling variables through the flow

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