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Default Value

What it does

Injects a default value for a field that exists on only one side (typically a field that's new in a later version) when converting into the side that lacks it. The direction converting away from the side that has it drops the real value — there's nowhere on the other side to put it.

When to use it

A field is genuinely new (or genuinely retired) between versions, has no equivalent on the other side, but you want objects converted into the side missing it to get a sane, working default rather than the field simply being absent — for instance, filling a new required field so converted objects still validate.

One direction is always lossy

If existsOn: Spoke (the field is new on the spoke, absent on the hub): converting hub → spoke injects the default (lossless — the hub never had a real value to preserve) and converting spoke → hub drops the real spoke value (lossy — the hub has nowhere to put it). This is inherent to the strategy, not a configuration mistake — acknowledgeLossy: true is always required.

Example

computeUnits exists only on the v1 spoke — the hub schema has no such field at all:

spec:
  properties:
    # no computeUnits field here
    storageGB:
      type: string

spec:
  properties:
    computeUnits:
      type: integer

Rule

- strategy: DefaultValue
  defaultValue:
    path: spec.computeUnits
    existsOn: Spoke
    default: 1
  acknowledgeLossy: true
  reason: >-
    computeUnits only exists on v1; converting a v1 object up to the hub
    and back down is fine, but hub-native objects converted down to v1
    get a sane default and lose nothing on the way back since the hub
    never had a real value to begin with.

Objects

A hub-native object, converted down to v1, gets the default injected:

spec:
  storageGB: "500"
  # (no computeUnits — the hub schema doesn't have this field)

spec:
  storageGB: "500"
  computeUnits: 1   # <- injected default

A v1-native object with a real computeUnits value, converted up to the hub, simply loses it (there's no hub field to put it in) — this is the acknowledged-lossy direction.

existsOn: Hub is the mirror case: the field exists only on the hub, and converting spoke → hub injects the default while hub → spoke drops the real value.