FabledCurator/alembic/versions/0088_reconcile_models_with_schema.py

"""Reconcile the database with what the models have always claimed (#3275).

Milestone 328 discovered ~130 places where the ORM models and the deployed
schema disagreed. Almost all of them were the MODEL being wrong — missing
`server_default`s, indexes and CHECK constraints that only ever existed in a
migration — and those are fixed in the model files with no DDL at all, because
the database already had them.

This migration carries the remainder — the two places where DDL is actually
needed, because the database is what is wrong.

`tag.fandom_id` is declared `index=True` on the model, but no migration ever
created that index. Every autogenerate run since would have proposed adding
it; nobody ran one, so the model and the database simply drifted apart and
stayed that way.

Deliberately NOT in this migration: anything about `image_record.sha256`. An
earlier draft of this file claimed sha256 was not unique in the database and
that duplicate rows were therefore possible. That was WRONG, and it was wrong
because it was read off `op.create_index("ix_image_record_sha256", ...)` at
0001 line 151 without reading line 149 two lines above it:

    sa.UniqueConstraint("sha256", name="uq_image_record_sha256"),

Uniqueness has been enforced since the initial schema. The database simply
expresses it as a CONSTRAINT plus a separate non-unique lookup index, where
the model expressed it as one `unique=True, index=True` column — the same
guarantee built from different objects, which is why the two schemas did not
line up. The model now declares the constraint and the plain index separately,
so it describes what is actually there. No DDL is needed for it.

Also here: six CHECK constraints whose names carry their table prefix TWICE.

`base.py`'s naming convention is `ck_%(table_name)s_%(constraint_name)s`, and
unlike the uq/fk/ix entries it applies even to a constraint that already has a
name. Six migrations passed an already-prefixed name, so the convention
prefixed it again:

    ck_external_link_ck_external_link_host
    ck_external_link_ck_external_link_status
    ck_import_settings_ck_import_settings_singleton
    ck_ml_settings_ck_ml_settings_singleton
    ck_post_ck_post_translation_override
    ck_tag_ck_tag_fandom_requires_character

Nothing reads a CHECK constraint by name, so this has never done any harm —
but it is exactly the development-era residue the collapsed baseline exists to
leave behind, and a public schema should not ship it. The models now declare
bare names, which the convention renders into the single-prefix form; this
renames the deployed constraints to match.

RENAME CONSTRAINT is a catalog-only operation: no table scan, no rewrite, no
validation of existing rows. It takes a brief ACCESS EXCLUSIVE lock and
returns. That is why this is safe to do on `post` and `tag`, which are the two
large tables in the schema.

Revision ID: 0088
Revises: 0087
Create Date: 2026-08-30

"""
from typing import Sequence, Union

from alembic import op

revision: str = "0088"
down_revision: Union[str, None] = "0087"
branch_labels: Union[str, Sequence[str], None] = None
depends_on: Union[str, Sequence[str], None] = None

# (table, doubled name, single-prefix name)
#
# Six, not the four a first read of the migrations turned up. The list that
# settles it is the one extracted from the chain's pg_dump by matching
# `ck_(\w+?)_ck_\1_` — reading the migrations by eye missed external_link
# twice over, in the same way an earlier pass missed a UNIQUE constraint two
# lines above the index it was looking at (see the sha256 note above).
DOUBLED_CHECKS = (
    ("external_link", "ck_external_link_ck_external_link_host",
     "ck_external_link_host"),
    ("external_link", "ck_external_link_ck_external_link_status",
     "ck_external_link_status"),
    ("import_settings", "ck_import_settings_ck_import_settings_singleton",
     "ck_import_settings_singleton"),
    ("ml_settings", "ck_ml_settings_ck_ml_settings_singleton",
     "ck_ml_settings_singleton"),
    ("post", "ck_post_ck_post_translation_override",
     "ck_post_translation_override"),
    ("tag", "ck_tag_ck_tag_fandom_requires_character",
     "ck_tag_fandom_requires_character"),
)


def _rename_check(table: str, old: str, new: str) -> None:
    # Guarded on pg_constraint rather than run bare: a database built from the
    # models (a fresh install, or the CI integration schema) already has the
    # single-prefix name, and this migration must be a no-op there rather than
    # an error. Same reasoning as the CREATE INDEX IF NOT EXISTS below.
    op.execute(
        f"""
        DO $$
        BEGIN
            IF EXISTS (
                SELECT 1 FROM pg_constraint
                WHERE conname = '{old}' AND conrelid = '{table}'::regclass
            ) THEN
                ALTER TABLE {table} RENAME CONSTRAINT {old} TO {new};
            END IF;
        END $$;
        """
    )


def upgrade() -> None:
    # IF NOT EXISTS because the index is what the model already asks for: any
    # database built from metadata rather than from this chain will have it,
    # and this migration must be a no-op there rather than an error.
    op.execute("CREATE INDEX IF NOT EXISTS ix_tag_fandom_id ON tag (fandom_id)")

    for table, old, new in DOUBLED_CHECKS:
        _rename_check(table, old, new)


def downgrade() -> None:
    for table, old, new in DOUBLED_CHECKS:
        _rename_check(table, new, old)

    op.execute("DROP INDEX IF EXISTS ix_tag_fandom_id")