New IDataProcessing interface that supports multiple DataElements and adding elements in response to changes

[ivarne]

Description

With support for subforms and multiple data models and the multiple PATCH endpoint, app developers want to read and write multiple data elements in a single request, and also to be able to ADD subform instances based on information changes in the main data element.

Deleting is different, because the current PATCH interface does not allow to signal deletion, and in addition it is likely better to have some sort of hidden mechanism so that the data isn't actually deleted until we trigger /process/next

Additional Information

Frontend will not yet support receiving new data elements in a PATCH response, and this needs to be added. If we want to support deletion of whole data elements, an appropriate interface needs to be negotiated. Likely solution would be to send instance.Data (or the full instance object)

[kentare]

Ref https://altinn.slack.com/archives/C02EJ9HKQA3/p1726137517047409

Gjentar behov vi har fra denne tråden:
Det er viktig at vi kan prefille med forskjellige verdier i datamodellen til subformen, vi gjør dette i dag i InstantiationProcessor. Vi gjør dette i dag med hjelp av gateways+InstantiationProcessor.

Casen er slik: Når instansen opprettes opprettes det et subform for Selskapsregnskap, denne prefilles med readonly data som er relevant til selskapsregnskapet ( i dag gjøres dette i InstantiationProcessor). Om en bruker svarer "JA" på en radiobutton (Skal konsernregnskap legges ved?) i skjemaet skal en subform (konsernregnskap) legges til med data som er readonly som omhandler konsernet. Dette er data som brukeren ikke kan legge inn selv eller endre på

[ivarne]

Fixed and available in 8.5.0-preview.4

• Support Extra data models and subforms in validation #730

The new interface is named IDataWriteProcessor