I have some idea to save sporadic measurements in a regular interval to a time series database but I'm not sure if that's the right approach or if there are better ones.
Some info:
I'm using node-red-contrib-huemagic to get the events from the hue motion sensor / hue lux sensor.
So whenever there is a motion that node "fires" and event but if there is no motion, there is no event / very sporadic and so nothing gets saved to the time series database ( in my case influxdb )
The node not only has a bool payload for motion, but also for daylight, dark which might be interesting at some point.
The main reason to have regular measurements is to have some nicer graphs with grafana and the discrete plugin. I also understand, that this includes the cost of using more disk space.
Since these hue nodes have no possibility to trigger them I wanted to save the values when there is an event using the context feature.
So whenever the context gets updated by a newer event, the newer values will be saved then.
Is that a good approach or am I totally on the wrong path.
I do exactly the same thing with influx to make sure the gap between samples is not too great. I use node-red-contrib-msg-resend which can be setup to keep resending the last message every 5 minutes (or whatever) till the next message arrives.
With InfluxDB and Grafana, you don't need to do this. I have similar records for things like my door bell and a digital sound sensor in the hall. But you don't need to do regular records because InfluxDB doesn't care - it is a time series DB so just records the time. It will work out averages and counts and whatever regardless. Grafana doesn't need anything special since you can simply tell it to use the previous value which will give you a continuous display as you would expect.
I had some problems using Previous Value in the Fill specifier, but I don't remember exactly what the problem was, I will have to carry out some experiments to see what it was. Does it pick up the previous value if there are no samples at all in the selected time range, in grafana for example?
I have determined the problems I have with using Fill(previous).
Firstly I like to have charts showing the time range Today. These start at midnight and show the complete day, with right hand side of the chart empty as it is in the future. If I use Fill(previous) then it fills the time from now to the end of the day with the latest values so I get horizontal lines to the right hand edge.
Secondly, if there are no samples at all for a field in the time range shown then it does not show the value from off the front of the chart. So for something like a setpoint that may not change for days the chart showing Today may not show the setpoint line at all.
I could not find a solution to those issues other than injecting repeat values into Influx occasionally.
The trick is to use the "Mapping" tab to map null to a default value. Probably false in the example above. On other examples it might be 0 or Off or whatever.
Been a while since I'd done it so I'd forgotten how.
I must be going blind, I cannot find a mapping tab anywhere. I found references to it on the older interface (with the tabs along the top) but cannot find it in the newer i/f.
Though I don't understand how, when viewing a time range with no samples for a field, this will show the current actual value (ie the last value before the start of the time range), I would have expected it to show the default value. But since I can't find where to set it I can't try it. Can someone point me in the right direction?
Can I just check, if you zoom in on a time range where there are no samples in the database for a field what do you see for that field? Also if you select Today as the time range what do you see for the time after the current time?
Note that the initial grey area is actually the value N/A because that's what this is set to, if you map null to 0 for example then you will get zero at the start of your display until a real value is written to the db.
I am not using the Discrete plugin, so it is not surprising that I don't see it
I am using the Graph panel. That explains some of our crossed wires.
Unfortunately showing zero or other default is not what I need. The use case is, for example, a room setpoint that only gets modified occasionally, maybe not for days, but I want to see it on the graph. I want it to show the actual value, not a default value so I can see how well the temperature control is working.
