Different amend approaches: in-place versioning vs changelog table

[sldblog]

Short problem statement; why is this a problem?

We have two approaches for tracking the "amend a referral" functionality.

Both approaches require us to retain the previous values for auditability to users and reporting.

1. First came the in-place versioning
2. Then we rolled out changelog and used in-place updating

Link to different approaches

1. Code using in-place versioning:

hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/ReferralService.kt

Lines 260 to 264 in fdf622d

	referralDetailsRepository.saveAndFlush(newDetails)
	if (existingDetails !== null && existingDetails !== newDetails) {
	existingDetails.supersededById = newDetails.id
	referralDetailsRepository.saveAndFlush(existingDetails)

2. Code using in-place updates:

hmpps-interventions-service/src/main/kotlin/uk/gov/justice/digital/hmpps/hmppsinterventionsservice/service/AmendReferralService.kt

Lines 62 to 65 in fdf622d

	referral.complexityLevelIds?.put(serviceCategoryId, update.complexityLevelId)
	val oldValue = ReferralAmendmentDetails(listOf(complexityLevel!!.toString()))
	val newValue = ReferralAmendmentDetails(listOf(update.complexityLevelId.toString()))

Do you have a proposed solution? Why?

Migrate everything to the changelog approach.

➕ Benefits: simplifies code and data model
➖ Drawbacks: bit complex to roll out in a zero-downtime environment