Improve existing and add new persistence filters

[J-N-K]

#2871 introduced working persistence filters base on time and threshold, but since they were never documented, I doubt they have been used at all.

This PR changes is API breaking because it changes the filter definitions in persistence.xtext but this will probably not be noticed at all. It also adds two new persistence filters: "Equals" and "NotEquals" that can be used to allow/disallow a certain set of values.

Filters can be defined by

Filters {
  tenseconds : T 10 s
  fivepercent : > % 5
  hundredmilliamps : > 100 mA
  equals : = "only","these","values"
  notequals : ! "not","these","values"

and be applied with

Items {
  item1, item2 : strategy = everyChange filter = fivepercent
  group1 : strategy = everyUpdate filter = tenseconds

I'll add documentation in the next few days.

[openhab-bot]

This pull request has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/is-the-a-way-to-persist-only-if-a-value-is-equal-or-not-equal-so-it-doesnt-graph-in-rrd4/146993/3

[rkoshak]

While you are at it, does it make sense to add a range filter? Ignore all values that are above/below a min/max range for filtering out obviously bogus sensor readings. That's a common use case.

One could argue that would best be applied in a profile I'll concede.

[kaikreuzer]

@J-N-K What do you think about @rkoshak suggestion above?

[J-N-K]

It's easy from code, the question is as @rkoshak already pointed out: is this something that should be done for persistence or is it more something for a profile? If you think it's useful as persistence filter, then I can add it.

[kaikreuzer]

I personally would consider it useful, because I often see the situation that bogus sensor values get persisted and there is no easy way to clean up persisted data afterwards. So if it is easy to implement and nobody vetos - why not add it.

[rkoshak]

I thought of a case that can only be solved as a persistence filter. What if you have a sensor where you do want to process errant readings in a rule (e.g. send an alert, take remedial action, etc.) but do not want to persist the data? If you used a profile you can't do that but as a persistence filter you can. (Or in a rule of course with the persist() action.

And it probably deserves it's own issue, but periodically users lament the fact that the persistence config doesn't allow something like "everything but". If I had two Items I don't want to be persisted but want all the rest to be, I have to include all the rest in the config instead of just the two to exclude.

That's not an easy change I suspect but is it something worth opening another issue for?

[kaikreuzer]

That's not an easy change I suspect but is it something worth opening another issue for?

Feel free to open one. 😄

[kaikreuzer]

lgtm, thanks!