Rules: Initialization of var DateTime fails; => How to solve?

[AndrewFG (Andrew Fiddian-Green)]

I need to implement a DateTime variable that records the previous time when a motion detector was activated. When OH is started this variable must be initialized to some value. I tried the following code at the top of the .rules file…

var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = now

… but this fails with the following error message; => so how can I initialize such a DateTime var without a failure? (note: using OH 2.5 latest release)

2019-12-27 14:51:29.223 [WARN ] [me.internal.engine.RuleContextHelper] - Variable 'Front_Bedroom_Motion_Detector_Last_Triggered' on rule file '24g.rules' cannot be initialized with value 'now': The name 'now' cannot be resolved to an item or type; line 44, column 61, length 3

[H102 (CM6.5 H102)]

The name ‘now’ cannot be resolved to an item or type

Make “now” a proxy item or give it a type.

[AndrewFG (Andrew Fiddian-Green)]

… or give it a type.

Thanks for the response, but how would I do that?

[H102 (CM6.5 H102)]

I’m not a rules guru but try:

var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = now as Number

Or

var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = new DateTime(localLastMeasurement_00.state.toString).toString("yyMMddHHmm")

See also these topics for dates, times, and motion:

DateTime Conversion

Overview In openHab there are different ways to handle Date/Time values. DateTimeType A DateTime Item carries a DateTimeType. Joda DateTime By default Rules use a Joda DateTime class to represent time, most notably now. Epoch The lowest common denominator when working with time is to get at the epoc value. Epoc is the number of milliseconds that has passed since 1 January 1970 GMT and stored in a long. With epoc, one can compare two dates together, convert a Joda DateTime to a DateTi…

Design Pattern: Motion Sensor Timer

Please see Design Pattern: What is a Design Pattern and How Do I Use Them for details on how to use DPs. Problem Statement Many motion detectors only report ON when they detect motion but do not send a corresponding OFF after no motion has been detected after a period of time. In addition, often one wants to control a device like a light for a certain period after the last motion is seen, not after the motion sensor goes to OFF. Therefore one needs to keep an occupancy Contact OPEN (or Switch O…

[AndrewFG (Andrew Fiddian-Green)]

I’m not a rules guru but try:

Hi @H102 many thanks for the suggestions. In the meantime, I also tried the following (which seems to work for me)…

var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = DateTime.now

PS I had already the examples that you cited; but they contained no information about initialization of var

[H102 (CM6.5 H102)]

Glad it’s working.

Please click the square box on solution post to mark topic solved.
Thanks

[rossko57]

When OH is started this variable must be initialized to some value.

You can set it to null and have your rules deal with that, as meaning “not yet known”

I tried the following code at the top of the .rules file

I do not think you can perform evaluations in the “global” context of a rules file, only assign constants.
So I was surprised that
var DateTime Front_Bedroom_Motion_Detector_Last_Triggered = DateTime.now
doesn’t throw an error.

Here’s the weird part though (which may not matter to you)
That doesn’t get evaluated at xxx.rules file load time. If you log it out some time after load, it gives that instant i.e. it gets evaluated at first use.
It’s a bit of a magic trick, but I can’t think of use for that.

I need to implement a DateTime variable that records the previous time when a motion detector was activated.

What most people do is use an Item. Added bonus, use persistence and have the genuine last value survive system reboots.

[AndrewFG (Andrew Fiddian-Green)]

I do not think you can perform evaluations in the “global” context of a rules file, only assign constants.

Hmm @rossko57 thank you for the interesting insights. I was wondering also how to make some rules execute conditionally depending a Boolean var that has been initialized as false as follows…

var Boolean isReadyToRun = new Boolean(false)

// rule A
when
..
then
  if (isReadyToRun) {}
end

// rule B
when
..
then
  ...
  isReadyToRun = true
end

Any thoughts on this?

[rossko57]

Looks fine.

You’ll find examples of most things around this forum

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[AndrewFG (Andrew Fiddian-Green)]

Hi @rossko57 many thanks for your inputs. I am running OH v2.5 openHabian on a Raspberry Pi machine, and I discovered, via your posts, that this build/version has a console configuration option “44” which allows to delay the loading of the .rules file by approximately 2 minutes. This prevents any var initialization errors, and gives time for the Things and Items to be loaded properly, before any rules are started. It works perfectly for me!