Migration

Defines a single migration that transforms data from one schema version to another.

A migration can operate at two different scopes:

• record: Transforms individual records, with optional filtering to target specific records
• store: Transforms the entire serialized store structure

Each migration has a unique ID and can declare dependencies on other migrations that must be applied first. The up function performs the forward transformation, while the optional down function can reverse the migration if needed.

type Migration = {
  readonly dependsOn?: readonly MigrationId[] | undefined
  readonly id: MigrationId
} & (
  | {
      readonly down?: (
        newState: SerializedStore<UnknownRecord>
      ) => SerializedStore<UnknownRecord> | void
      readonly scope: 'store'
      readonly up: (
        oldState: SerializedStore<UnknownRecord>
      ) => SerializedStore<UnknownRecord> | void
    }
  | {
      readonly down?: (newState: UnknownRecord) => UnknownRecord | void
      readonly filter?: (record: UnknownRecord) => boolean
      readonly scope: 'record'
      readonly up: (oldState: UnknownRecord) => UnknownRecord | void
    }
)