feat: add Alembic

This adds the `ratings_index` to code, which so far wasn't reflected in
SQLAlchemy's metadata.

alembic/env.py

@@ -0,0 +1,103 @@
+import asyncio
+from logging.config import fileConfig
+
+import sqlalchemy as sa
+from sqlalchemy import pool
+from sqlalchemy.engine import Connection
+from sqlalchemy.ext.asyncio import async_engine_from_config
+
+from alembic import context
+from unwind import db, models
+
+# this is the Alembic Config object, which provides
+# access to the values within the .ini file in use.
+config = context.config
+
+# Interpret the config file for Python logging.
+# This line sets up loggers basically.
+if config.config_file_name is not None:
+    fileConfig(config.config_file_name)
+
+
+def is_different_type(
+    context,
+    inspected_column: sa.Column,
+    metadata_column: sa.Column,
+    inspected_type: sa.types.TypeEngine,
+    metadata_type: sa.types.TypeEngine,
+) -> bool | None:
+    # We used "TEXT" in our manual SQL, which in SQLite is the same as VARCHAR, but
+    # for SQLAlchemy/Alembic looks different.
+    equiv_types = [(sa.TEXT, sa.String)]
+    for types in equiv_types:
+        if isinstance(inspected_type, types) and isinstance(metadata_type, types):
+            return False
+    return None  # defer to default compare implementation
+
+
+def run_migrations_offline() -> None:
+    """Run migrations in 'offline' mode.
+
+    This configures the context with just a URL
+    and not an Engine, though an Engine is acceptable
+    here as well.  By skipping the Engine creation
+    we don't even need a DBAPI to be available.
+
+    Calls to context.execute() here emit the given string to the
+    script output.
+
+    """
+    context.configure(
+        url=db._connection_uri(),
+        target_metadata=models.metadata,
+        literal_binds=True,
+        dialect_opts={"paramstyle": "named"},
+        compare_type=is_different_type,
+        render_as_batch=True,
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+def do_run_migrations(connection: Connection) -> None:
+    context.configure(
+        connection=connection,
+        target_metadata=models.metadata,
+        compare_type=is_different_type,
+        render_as_batch=True,
+    )
+
+    with context.begin_transaction():
+        context.run_migrations()
+
+
+async def run_async_migrations() -> None:
+    """In this scenario we need to create an Engine
+    and associate a connection with the context.
+
+    """
+
+    connectable = async_engine_from_config(
+        config.get_section(config.config_ini_section, {}),
+        prefix="sqlalchemy.",
+        url=db._connection_uri(),
+        poolclass=pool.NullPool,
+    )
+
+    async with connectable.connect() as connection:
+        await connection.run_sync(do_run_migrations)
+
+    await connectable.dispose()
+
+
+def run_migrations_online_async() -> None:
+    """Run migrations in 'online' mode."""
+
+    asyncio.run(run_async_migrations())
+
+
+if context.is_offline_mode():
+    run_migrations_offline()
+else:
+    run_migrations_online_async()