conditional defaults

[pljakobs]

Is there possibly already a way of having conditional defaults for configdb?
I'm adding a telemetry function to my firmware (I am seeing uncommanded reboots in the field and want to be able to troubleshoot them) and for that, I've added a mttq based telemetry that I want to default to on for debug builds but to off for release builds.
Is that something that could be done in configdb?

my schema snippet looks like this:

   "debug": {
      "type": "object",
      "properties": {
        "enabled": {
          "type": "boolean",
          "default":true
        },
        "server": {
          "type": "string",
          "default":"lightinator.de:1883"
        }
      }

[mikee47]

There is currently no support for such conditional defaults. In this case may I suggest the simplest solution is to set defaults for a release build ("default": false) then include some conditionally compiled code to override it. At present I think that would involve checking for the existence of the relevant store backing file, and if it doesn't exist you can just change the value to true.

I guess it would be nice if there were a callback or similar which the application could use to return custom defaults. This happens in Database.cpp line 193...

A more generic solution might be to support pre-processing with some kind of expression parsing or expression substitution such as "default": %false if SMING_RELEASE else true%. That should probably be done outside of dbgen.py so (a) it always gets valid JSON, and (b) the post-processed schema is available for inspection.

[mikee47]

Or maybe add a flag/method to determine if an object or store is using defaults...

[pljakobs]

I'm currently defining those items as ENUM with an UNDEF/TRUE/FALSE choice and, if they're UNDEF, set them upon first access. That works, but having this part of the build system would be nicer.
But as far as I could find, there's no json schema support for that, so it would be a proprietary extension.