The t/0 map shape emitted by PhoenixKit.Migrations.ExpectedSchema.data_invariants/1 — an assertion about data, not schema, for an upgrade-only transform the squash baseline cannot replay (spec §5.1/§8.3's minimum set: post-V114 no composite "integration:*" settings keys, V137 aws_message_id uniqueness, V77/V109 renamed-key absence, and similar).

Schema objects (PhoenixKit.Migrations.ExpectedSchema.Object) answer "does this table/column/index/... exist with the right shape". Data invariants answer a question no catalog lookup can: "did the data that already lived in this table get correctly transformed", for transforms a fresh baseline never runs (a fresh install has no legacy rows to rename/dedupe/rewrite in the first place — the invariant is vacuously true there) but an incrementally-upgraded install must have already satisfied via the real chain's delta modules.

Usage

Report-only, always — verify surfaces a failing invariant as an error-severity divergence (spec §6.2's severity mapping) but repair never attempts to fix one (there is no additive SQL that undoes a settings-key rename or a dedup-delete safely outside the chain). The one place a data invariant gates a decision rather than merely reporting is --adopt (spec §6.4 R4): stamping the floor version on a half-installed/adopted database is refused unless every floor-level invariant (since <= floor) holds, exactly like the verify pass's own :missing/error-severity gate.

Fields

• :since — the version whose delta module the invariant characterizes (used the same way Object.t()'s :since gates object creation: an invariant with since > comment has not "happened" yet for that DB and is not evaluated).
• :desc — human-readable, one line, printed verbatim in reports.
• :assert — SQL text that returns exactly one row with one boolean column; true means the invariant holds. Carries the same "__SCHEMA__" token (PhoenixKit.Migrations.ExpectedSchema.Object.schema_token/0) as Object.t()'s :check/:create strings — substitute it via materialize/2, never by hand.

Example

iex> invariant = %{
...>   since: 114,
...>   desc: "V114: settings integration rows are uuid-keyed",
...>   assert: "SELECT NOT EXISTS (SELECT 1 FROM __SCHEMA__.phoenix_kit_settings " <>
...>             "WHERE key LIKE 'integration:%')"
...> }
iex> DataInvariant.materialize(invariant, "auth").assert
"SELECT NOT EXISTS (SELECT 1 FROM auth.phoenix_kit_settings WHERE key LIKE 'integration:%')"