Align GasConsumption.read_at to represent the start of hour

[dennissiemensma]

Originally reported by: Dennis Siemensma (Bitbucket: dennissiemensma, GitHub: dennissiemensma)

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Currently GasConsumption.read_at represents the passed hour read, so the end timestamp of the hour. We should make that the start of the hour instead.

Now

read_at = 22:00 = reading was between 21:00 and 22:00

Aligned

read_at = 21:00 = reading was between 21:00 and 22:00

Should not be very hard to alter, as migrations will be easy in the database (-1 hour).

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• Bitbucket: https://bitbucket.org/dennissiemensma/dsmr-reader/issue/40

[dennissiemensma]

Very nice F() field:

    GasConsumption.objects.all().update(
        read_at=models.F('read_at') + timezone.timedelta(hours=hours_offset)
    )

[dennissiemensma]

Running across a bug where statistics generation is halted when no gas data is found.

[dennissiemensma]

Fixed it, by making gas optional, which was required anyway due to #34

[dennissiemensma]

Refactored a bit so the ORM's queries made more sense:

MySQL:

(0.028) UPDATE `dsmr_consumption_gasconsumption` SET `read_at` = (`dsmr_consumption_gasconsumption`.`read_at` - INTERVAL '0 0:0:3600:0' DAY_MICROSECOND); args=()

PostgreSQL:

(0.027) UPDATE "dsmr_consumption_gasconsumption" SET "read_at" = ("dsmr_consumption_gasconsumption"."read_at" - '0 days 3600.000000 seconds'::interval); args=(datetime.timedelta(0, 3600),)

[dennissiemensma]

Merged, along with bugfix for #50.

[dennissiemensma]

Deployed.

[dennissiemensma]

I've seem to have created a bug in calculating gas consumption, using the new logic.

• When affected by the bug, the dashboard gas graph will no longer display usage.
• The day usage (= diff) is however unaffected.

At least we still have te source readings to recalculate the consumption retroactive.

[dennissiemensma]

Fixed bug and added migration to recalculate incorrect data.