A guide to understanding 'Persistent Context'

[zenofmud]

I'm not sure what you mean by:

@Hunter

deletion of stored data is still not included as default option

You can use a change node with the `delete option

[Nodi.Rubrum]

One of the funniest, accurate explanations of null vs. delete vs. empty (zero), etc... I have ever seen is below... and I discovered it in this forum!

[msongz]

very helpful for understand how to persistent context,
and this article link should sit inside the template node's help!!!

[Colin]

Welcome to the forum @msongz

The problem is that context can (and is) used with virtually all nodes, not just the template node. In fact I don't think I have ever used it in a template node. The most common use is probably in the Function node.

[Paul-Reed]

In case it helps anyone, here is a link to a useful example by @Steve-Mcl
Also read down that thread to find out about saving a context object by 'reference'

Saving a single value to context

{ "192.168.1.10": { "last_on": 1622751269764, "last_off": 1622751272068 }, "192.16.1.13": { "last_on": 1622751772269, "last_off": 1622751774284 } } Working demo updating the values of the objects properties... [{"id":"4d40b13c.c8309","type":"function","z":"1bd2b382.4dd4f4","name":"setup demo data","func":"msg.payload = {\n \"192.168.1.10\": {\n \"last_on\": 1622751269764,\n \"last_off\": 1622751272068\n },\n \"192.16.1.13\": {\n \"las…

[u20p17]

Hi all,
I am trying to modify the settings.js like in this post:

@Lost

contextStorage: {
File : { module: "localfilesystem"},
default : { module: "memory" }
},

Therefore I started Node-Red and checked the log where the file is stored:

start
> node $NODE_OPTIONS node_modules/node-red/red.js "--settings" "/etc/node-red/config.js"
4 Jan 09:53:03 - [info] 
Welcome to Node-RED
===================
4 Jan 09:53:03 - [info] Node-RED version: v2.1.4
4 Jan 09:53:03 - [info] Node.js  version: v16.13.1
4 Jan 09:53:03 - [info] Linux 5.10.63-v8 arm64 LE
4 Jan 09:53:05 - [info] Loading palette nodes
4 Jan 09:53:11 - [info] Dashboard version 3.1.3 started at /endpoint/ui
4 Jan 09:53:14 - [info] Settings file  : /etc/node-red/config.js
4 Jan 09:53:14 - [info] Context store  : 'default' [module=memory]
4 Jan 09:53:14 - [info] User directory : /config/node-red/
4 Jan 09:53:14 - [warn] Projects disabled : editorTheme.projects.enabled=false
4 Jan 09:53:14 - [info] Flows file     : /config/node-red/flows.json
4 Jan 09:53:15 - [info] Server now running at http://127.0.0.1:46836/
4 Jan 09:53:15 - [info] Starting flows

As you can see it should be stored in /etc/node-red/config.js, but I can not find this folder. I connected via ssh and logged in with root and the pw.but I can not find the file:

What could be the problem?

Thanks

[Steve-Mcl]

Have you looked in /config/node-red/?

Also, have you saved any values in file context?

[zenofmud]

Since you have the default set to memory, you need to specify when you want it to be saved into the file. For example, in a change node you will have to pick the 'File' option

or it will default to memory.

If you want it to default to the filesystem, change the settings.js to

     	contextStorage: {
			default    : { module: "localfilesystem" },
 			memory     : { module: "memory" }
     	},

EDIT: you should also read Working with context : Node-RED
and Writing Functions : Node-RED

[TotallyInformation]

@u20p17

As you can see it should be stored in /etc/node-red/config.js, but I can not find this folder.

It is only there because that's where you told it you wanted it to be when you started Node-RED - line 2 of your output. I don't believe that is a normal option for a default installation of Node-RED. How did you install Node-RED?

What happens if you do cd /etc/node-red? Do you get an error?