Skip to content

Constant

What it does

Forces a field that exists on only one side to a fixed, hard-coded value — not derived from anything on the other side. The direction converting away from the side that has it drops the real value, exactly like Default Value, except the injected value is always the same constant rather than a schema default.

When to use it

A field is a bookkeeping/versioning marker that should always read a specific fixed value at a given version, regardless of what (if anything) was ever set — a schema-version tag being the canonical example.

One direction is always lossy

Same shape as Default Value: the direction that injects the constant is lossless (nothing real is being overwritten with useful information — it's a marker), and the direction converting away from the side that has it drops whatever real value was there, which is always lossy and always requires acknowledgeLossy: true.

Example

schemaVersion exists only on the v2 spoke, and is always forced to the literal string "v2" regardless of anything else:

spec:
  properties:
    # no schemaVersion field
    storageGB:
      type: string

spec:
  properties:
    schemaVersion:
      type: string

Rule

- strategy: Constant
  constant:
    path: spec.schemaVersion
    existsOn: Spoke
    value: "v2"
  acknowledgeLossy: true
  reason: >-
    schemaVersion is a v2-only bookkeeping field; its value is always
    forced to "v2" and carries no information worth round-tripping
    through the hub.

Objects

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

spec:
  storageSize: "500"
  schemaVersion: "v2"   # <- always this constant, regardless of input

Even if a v2-native object is created with schemaVersion: "some-other-value", converting up to the hub and back down always yields schemaVersion: "v2" — the original value is discarded, matching the acknowledged-lossy direction.