How to initialize 'derived' items once real values become known?

[rlkoshak (Rich Koshak)]

@bosschaert

I have some items that are not bound directly to a device/channel but that are used by one of my rules to drive multiple devices

Commonly referred to around here as Proxy Items.

@bosschaert

How can I improve my setup so that on restart from openhab these derived items are properly initialized based on actual device values as they come in?

Two things:

1. Set up persistence and restoreOnStartup for the proxy items. When OH restarts the Item will be initialized to whatever it happened to be when OH went down. This isn’t full proof of course because the state of the devices could have changed while OH was down but it will cover 90-95% of the cases.

2. Create a rule that triggers when the radiators report their state and recalculate the value of your proxy Item.

Without seeing your actual Items I can’t say for sure, but you might be able to use a Group instead of a proxy Item in this case. Assuming your radiator Items are Numbers your Group would look something like:

Group:Number:MAX BedroomRadiators

Assign all the applicable bedroom radiators to this Group and the state of the Group itself will be the maximum of all its members. Any command that gets sent to the Group will be forwarded to all its members.

MIN might also make sense in this case as well. But again, without seeing the actual Items or getting more info about what you want to happen when for whatever reason all of the radiators are not set to the same state.