Replicant.SchemaChange (Replicant v0.1.0)

Classification of a Relation diff (spec §9): additive (new column — auto-apply) or destructive (dropped column, type change, replica-identity change — delegate to the sink or halt fail-closed). A Truncate is delivered as a change, not a schema change.

The Assembler diffs each incoming Relation against the cached one and calls classify/2. nil means "no schema-relevant change" (e.g. only column order shifted without drops/type/identity changes — treated as additive-safe).

Replica-identity changes (spec §7/§9)

A change of replica identity is destructive because it alters the meaning of old_record for every subsequent change. classify/2 catches it two ways: the replica_identity enum value changing (:default -> :all_columns), AND the set of :key-flagged columns changing while the enum is unchanged (a REPLICA IDENTITY USING INDEX swap to a different unique index, or a primary-key change that keeps the same column names). Both classify :replica_identity_changed :destructive.

Summary

Types

change()

kind()

t()

Functions

classify(old, new)

Diff old and new Relation messages. Returns %SchemaChange{} or nil when nothing schema-relevant changed. A replica-identity change dominates (checked first) because it alters the meaning of old_record for every subsequent change.

Types

change()

@type change() ::
  :column_added | :column_dropped | :type_changed | :replica_identity_changed

kind()

@type kind() :: :additive | :destructive

t()

@type t() :: %Replicant.SchemaChange{
  change: change(),
  detail: String.t() | nil,
  kind: kind(),
  schema: String.t() | nil,
  table: String.t() | nil
}

Functions

classify(old, new)

@spec classify(
  Replicant.Decoder.Messages.Relation.t() | nil,
  Replicant.Decoder.Messages.Relation.t()
) ::
  t() | nil