Support multipart saving

[olemartinorg]

Description

After Altinn/app-frontend-react/pull/899 is merged, multipart saving will be implemented in app-frontend-react. This means that the PUT request for saving the data model can start sending multipart bodies containing not just the datamodel we want to save, but also the paths inside that datamodel that changed (along with their previous values).

As an example, here is a request we might send. I've added whitespace to the JSON for readability, although we won't send that in practice.

PUT /org/app/instances/512345/uuid/data/uuid
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryyWYh3C7EIYlu8pJj

------WebKitFormBoundaryyWYh3C7EIYlu8pJj
Content-Disposition: form-data; name="dataModel"

{
  "skjemanummer": "1603",
  "spesifikasjonsnummer": "12392",
  "blankettnummer": "RF-1366",
  "tittel": "Endringsmelding",
  "gruppeid": "9785",
  "Endringsmelding-grp-9786": {
    "Avgiver-grp-9787": {
      "KontaktpersonEPost-datadef-27688": {
        "value": "Ja"
      }
    },
    "OversiktOverEndringene-grp-9788": [
      {
        "SkattemeldingEndringEtterFristOpprinneligBelop-datadef-37131": {
          "value": "1"
        }
      }
    ]
  }
}
------WebKitFormBoundaryyWYh3C7EIYlu8pJj
Content-Disposition: form-data; name="previousValues"

{
  "Endringsmelding-grp-9786.OversiktOverEndringene-grp-9788[0].SkattemeldingEndringEtterFristOpprinneligBelop-datadef-37131.value": null
}
------WebKitFormBoundaryyWYh3C7EIYlu8pJj--

You now get two objects, not just one:

1. The dataModel (always named as such, regardless of the data model name - which we don't really know or care about in app-frontend). This is the same object we used to send.
2. The previousValues map. This uses dot-notation to indicate a path inside the data model that changed. For every item that changed, the previous value is listed as the map value. If the path did not exist before, the value will be null.

The above example contains a path inside a repeating group that changed - specifically on row 0.

Another interesting example is seen here. I added 3 rows, with the following values:

1. 1 and 2
2. 3 and 4
3. 5 and 6

Then I deleted the second row (containing the values 3 and 4), which leads to this request:

PUT /org/app/instances/512345/uuid/data/uuid
Content-Type: multipart/form-data; boundary=----WebKitFormBoundaryBkzRPylfSvVRa1ym

------WebKitFormBoundaryBkzRPylfSvVRa1ym
Content-Disposition: form-data; name="dataModel"

{
  "skjemanummer": "1603",
  "spesifikasjonsnummer": "12392",
  "blankettnummer": "RF-1366",
  "tittel": "Endringsmelding",
  "gruppeid": "9785",
  "Endringsmelding-grp-9786": {
    "Avgiver-grp-9787": {
      "KontaktpersonEPost-datadef-27688": {
        "value": "Ja"
      }
    },
    "OversiktOverEndringene-grp-9788": [
      {
        "SkattemeldingEndringEtterFristOpprinneligBelop-datadef-37131": {
          "value": "1"
        },
        "SkattemeldingEndringEtterFristNyttBelop-datadef-37132": {
          "value": "2"
        }
      },
      {
        "SkattemeldingEndringEtterFristOpprinneligBelop-datadef-37131": {
          "value": "5"
        },
        "SkattemeldingEndringEtterFristNyttBelop-datadef-37132": {
          "value": "6"
        }
      }
    ]
  }
}
------WebKitFormBoundaryBkzRPylfSvVRa1ym
Content-Disposition: form-data; name="previousValues"

{
  "Endringsmelding-grp-9786.OversiktOverEndringene-grp-9788[1].SkattemeldingEndringEtterFristOpprinneligBelop-datadef-37131.value": "3",
  "Endringsmelding-grp-9786.OversiktOverEndringene-grp-9788[1].SkattemeldingEndringEtterFristNyttBelop-datadef-37132.value": "4",
  "Endringsmelding-grp-9786.OversiktOverEndringene-grp-9788[2].SkattemeldingEndringEtterFristOpprinneligBelop-datadef-37131.value": "5",
  "Endringsmelding-grp-9786.OversiktOverEndringene-grp-9788[2].SkattemeldingEndringEtterFristNyttBelop-datadef-37132.value": "6"
}
------WebKitFormBoundaryBkzRPylfSvVRa1ym--

Notice that the row indexes 1 and 2 had changed (row 0 did not change). Index 1 used to have the values 3 and 4 (but from the data model we can tell they now have the values 5 and 6), while index 2 used to have the values 5 and 6 (but index 2 no longer exists in the data model).

Other things to be aware of:

• As an app developer, I would expect to have a somewhat rich interface to interact with this information (the raw data is a bit cumbersome to work with). I.e., a way to get a list of "changes" with previous/new values.
• For this feature to work with app-frontend, the backend needs to inform that the multiPartSave feature is enabled (see FeatureSet #188).
• The headers we used to send (X-DataField and X-ComponentId) are no longer passed to the backend when multipart saving is enabled. It is advised that app developers can choose to enable multipart saving when they are ready for it, although we should encourage them to do so (possibly also updating the template to enable the feature by default for new apps).

Additional Information

• Repeating groups: ProcessDataWrite mangler info om hva som har trigget eventet app-frontend-react#810
• Saving datamodel along with list of changed fields and previous values app-frontend-react#899 (client-side implementation)