Prepare persistence to be ready for QuantityTypes

[cweitkamp]

Most methods provided by PersistenceExtension e.g. sumSince(), averageSince() or deltaSince() are calculating results by simply casting everything to DecimalType internally. But some queryable persistence services return QuantityType values too. The calculations on the one hand should be able to deal with unit conversion on the other hand should not return a DecimalType result.

See eclipse-archived/smarthome#5675 (comment)

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Related issues which will be fixed once this feature has been implemented in all persistence add-ons: #669 and #1379

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• RRD4J: PR [rrd4j] Correctly identify Number items with dimensions and persist them in the defined unit openhab-addons#8866 and [rrd4j] Return QuantityTypes for number items with dimension openhab-addons#8938

• JDBC: PR [jdbc] Return QuantityTypes for number items with dimension openhab-addons#9426

• DynamoDB: PR [dynamodb] Dynamodb QuantityType and data expiration (TTL) support. AWS SDK updated openhab-addons#9937

• INFULXDB: open issue [influxdb] OH3.0.0 Persisted values are restored from Influx without UoM openhab-addons#9578

• Changes in PersistenceExtension

[ssalonen]

@cweitkamp you can refer to openhab/openhab-addons#9606 for DynamoDB UoM support.

[cweitkamp]

@ssalonen Done. I guess you will pick it up yourself in the near future. Thanks.

[ssalonen]

Thanks, will do.

Do I understand correctly that persistence and queries work with quantitypes already just fine if the support is there in the persistence service?

However, the utility functions like average do not support units correctly, and this issue is about fixing that.

[cweitkamp]

Yes, exactly. We have three things to do.

1. Persistence services must add support for returning QuantityType values. How the implementation will look like depends on the persistence service itself. e.g. the implementation in [jdbc] Return QuantityTypes for number items with dimension openhab-addons#9426 could be done completely different by extending the database structure and add a column for unit of number items.
2. The internal calculation for methods like sumSince(), averageSince() or deltaSince() should distinguish between different types. Which means for UoM to convert all values to the same unit before doing the math.
3. The return value of some methods has to be changed. In which way is not yet fixed.

Where 1. and 2. are imo straight forward enhancements 3. may result in a breaking change.

[ssalonen]

DynamoDB support for QuantityType implemented in openhab/openhab-addons#9937