TASK-023: Make database migrations atomic
Replace non-atomic db.executescript() with explicit transaction control. Wrap each migration's DDL statements and schema_migrations insert in a single BEGIN IMMEDIATE ... COMMIT transaction to ensure atomicity. Changes: - Add _parse_migration_statements() to split migration scripts into individual statements while handling comments and string literals - Update _apply_migration() to wrap all statements in a single explicit transaction with rollback on error - Ensure _get_current_schema_version() uses execute() instead of executescript() - Add 9 new tests for migration atomicity and statement parsing - Update Backend-Development.md with migration authoring guidelines If a crash occurs between DDL execution and schema_migrations insert, the next startup will re-apply the entire migration atomically, preventing partial migrations and data corruption. Test coverage: 98% on db.py (up from 55%) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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@@ -142,7 +142,7 @@ async def _configure_connection(db: aiosqlite.Connection) -> None:
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async def _get_current_schema_version(db: aiosqlite.Connection) -> int:
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"""Return the highest applied schema version for the given database."""
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await db.executescript(_CREATE_SCHEMA_MIGRATIONS)
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await db.execute(_CREATE_SCHEMA_MIGRATIONS)
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async with db.execute("SELECT MAX(version) FROM schema_migrations;") as cursor:
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row = await cursor.fetchone()
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if row is None or row[0] is None:
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@@ -150,12 +150,114 @@ async def _get_current_schema_version(db: aiosqlite.Connection) -> int:
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return int(row[0])
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async def _parse_migration_statements(script: str) -> list[str]:
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"""Parse a migration script into individual SQL statements.
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Splits on semicolons but ignores semicolons inside string literals and
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comments. Handles both block (-- comment) and line comments.
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Args:
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script: The raw migration script.
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Returns:
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List of SQL statements (stripped of whitespace and comments).
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"""
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statements: list[str] = []
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current_stmt: list[str] = []
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i = 0
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while i < len(script):
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char = script[i]
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# Skip block comments (-- ...)
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if i < len(script) - 1 and script[i:i+2] == "--":
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while i < len(script) and script[i] != "\n":
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i += 1
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i += 1
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continue
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# Skip line comments (/* ... */)
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if i < len(script) - 1 and script[i:i+2] == "/*":
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i += 2
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while i < len(script) - 1:
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if script[i:i+2] == "*/":
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i += 2
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break
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i += 1
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continue
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# Handle string literals (single or double quotes)
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if char in ("'", '"'):
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quote = char
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current_stmt.append(char)
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i += 1
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while i < len(script):
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if script[i] == quote:
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if i + 1 < len(script) and script[i + 1] == quote:
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# Escaped quote
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current_stmt.append(quote)
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current_stmt.append(quote)
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i += 2
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else:
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# End of string
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current_stmt.append(quote)
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i += 1
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break
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else:
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current_stmt.append(script[i])
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i += 1
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continue
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# Statement separator
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if char == ";":
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stmt = "".join(current_stmt).strip()
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if stmt:
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statements.append(stmt)
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current_stmt = []
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i += 1
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continue
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current_stmt.append(char)
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i += 1
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# Add any remaining statement
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stmt = "".join(current_stmt).strip()
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if stmt:
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statements.append(stmt)
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return statements
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async def _apply_migration(db: aiosqlite.Connection, version: int) -> None:
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"""Apply a single migration step and record its completion."""
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"""Apply a single migration step and record its completion atomically.
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Wraps all DDL statements and the schema_migrations insert in a single
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BEGIN IMMEDIATE ... COMMIT transaction to ensure atomicity. If any
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statement fails, the entire migration is rolled back.
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Args:
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db: An open aiosqlite.Connection.
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version: The migration version number.
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Raises:
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Any exception from executing the migration statements or inserting
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the schema migration record will cause a rollback.
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"""
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migration_script = _MIGRATIONS[version]
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await db.executescript(migration_script)
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await db.execute("INSERT INTO schema_migrations (version) VALUES (?);", (version,))
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await db.commit()
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statements = await _parse_migration_statements(migration_script)
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try:
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await db.execute("BEGIN IMMEDIATE;")
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for statement in statements:
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await db.execute(statement)
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await db.execute("INSERT INTO schema_migrations (version) VALUES (?);", (version,))
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await db.commit()
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except Exception:
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await db.rollback()
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raise
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async def _migrate_schema(db: aiosqlite.Connection) -> None:
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@@ -1,9 +1,16 @@
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import asyncio
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from pathlib import Path
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from unittest.mock import AsyncMock, patch
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import aiosqlite
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import pytest
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from app.db import open_db
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from app.db import (
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_apply_migration,
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_parse_migration_statements,
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init_db,
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open_db,
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)
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async def test_open_db_applies_hardening_pragmas(tmp_path: Path) -> None:
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@@ -56,3 +63,181 @@ async def test_open_db_respects_busy_timeout_for_concurrent_writes(tmp_path: Pat
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assert row is not None and row[0] == "locked"
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finally:
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await connection_a.close()
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async def test_parse_migration_statements_single_statement() -> None:
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"""Test parsing a single statement without comments."""
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script = "CREATE TABLE test (id INTEGER PRIMARY KEY);"
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statements = await _parse_migration_statements(script)
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assert len(statements) == 1
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assert statements[0] == "CREATE TABLE test (id INTEGER PRIMARY KEY)"
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async def test_parse_migration_statements_multiple_statements() -> None:
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"""Test parsing multiple statements separated by semicolons."""
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script = """
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CREATE TABLE test (id INTEGER PRIMARY KEY);
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CREATE INDEX idx_test ON test(id);
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"""
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statements = await _parse_migration_statements(script)
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assert len(statements) == 2
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assert "CREATE TABLE test" in statements[0]
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assert "CREATE INDEX idx_test" in statements[1]
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async def test_parse_migration_statements_with_line_comments() -> None:
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"""Test parsing statements with line comments."""
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script = """
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-- This is a comment
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CREATE TABLE test (id INTEGER PRIMARY KEY);
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-- Another comment
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"""
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statements = await _parse_migration_statements(script)
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assert len(statements) == 1
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assert "CREATE TABLE test" in statements[0]
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async def test_parse_migration_statements_with_block_comments() -> None:
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"""Test parsing statements with block comments."""
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script = """
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/* Block comment */
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CREATE TABLE test (id INTEGER PRIMARY KEY);
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/* Another block */
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"""
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statements = await _parse_migration_statements(script)
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assert len(statements) == 1
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assert "CREATE TABLE test" in statements[0]
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async def test_parse_migration_statements_with_string_literals() -> None:
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"""Test parsing statements with string literals containing semicolons."""
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script = """
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CREATE TABLE test (id INTEGER PRIMARY KEY, data TEXT);
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INSERT INTO test (data) VALUES ('value; with; semicolons');
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"""
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statements = await _parse_migration_statements(script)
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assert len(statements) == 2
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assert "CREATE TABLE test" in statements[0]
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assert "INSERT INTO test" in statements[1]
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assert "value; with; semicolons" in statements[1]
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async def test_parse_migration_statements_with_escaped_quotes() -> None:
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"""Test parsing statements with escaped quotes in string literals."""
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script = """
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INSERT INTO test (data) VALUES ('it''s a test');
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"""
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statements = await _parse_migration_statements(script)
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assert len(statements) == 1
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assert "it''s a test" in statements[0]
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async def test_apply_migration_is_atomic_success(tmp_path: Path) -> None:
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"""Test that migration is atomic when all statements succeed."""
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database_path = str(tmp_path / "bangui_atomic.db")
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db = await open_db(database_path)
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try:
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# Initialize schema_migrations table
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await db.execute(
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"CREATE TABLE IF NOT EXISTS schema_migrations (version INTEGER PRIMARY KEY, migrated_at TEXT);"
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)
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await db.commit()
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# Apply a test migration
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await _apply_migration(db, 1)
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# Verify the migration was recorded
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async with db.execute(
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"SELECT version FROM schema_migrations WHERE version = 1;"
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) as cursor:
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row = await cursor.fetchone()
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assert row is not None and row[0] == 1
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# Verify the schema tables exist
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async with db.execute(
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"SELECT name FROM sqlite_master WHERE type='table' AND name='settings';"
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) as cursor:
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row = await cursor.fetchone()
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assert row is not None
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finally:
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await db.close()
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async def test_apply_migration_is_atomic_rollback(tmp_path: Path) -> None:
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"""Test that migration is rolled back when a statement fails.
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This test verifies that when an error occurs mid-migration, the
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transaction is rolled back and the schema_migrations table is NOT updated.
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"""
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database_path = str(tmp_path / "bangui_rollback.db")
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db = await open_db(database_path)
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try:
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# Initialize schema_migrations table
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await db.execute(
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"CREATE TABLE IF NOT EXISTS schema_migrations (version INTEGER PRIMARY KEY, migrated_at TEXT);"
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)
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await db.commit()
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# Create a custom migration that will fail
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from app import db as db_module
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original_migrations = db_module._MIGRATIONS.copy()
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# Add a migration that will fail on the second statement
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db_module._MIGRATIONS[99] = """
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CREATE TABLE test_rollback (id INTEGER PRIMARY KEY);
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INSERT INTO nonexistent_table VALUES (1);
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"""
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try:
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# Attempt migration; it should fail
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with pytest.raises(Exception): # sqlite3 will raise an error
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await _apply_migration(db, 99)
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# Verify the migration was NOT recorded
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async with db.execute(
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"SELECT version FROM schema_migrations WHERE version = 99;"
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) as cursor:
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row = await cursor.fetchone()
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assert row is None
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# Verify the test table was NOT created (rollback occurred)
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async with db.execute(
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"SELECT name FROM sqlite_master WHERE type='table' AND name='test_rollback';"
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) as cursor:
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row = await cursor.fetchone()
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assert row is None
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finally:
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# Restore original migrations
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db_module._MIGRATIONS = original_migrations
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finally:
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await db.close()
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async def test_init_db_idempotent(tmp_path: Path) -> None:
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"""Test that init_db is idempotent."""
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database_path = str(tmp_path / "bangui_idempotent.db")
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db = await open_db(database_path)
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try:
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# Initialize once
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await init_db(db)
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# Get schema version
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async with db.execute(
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"SELECT MAX(version) FROM schema_migrations;"
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) as cursor:
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row1 = await cursor.fetchone()
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# Initialize again (should be no-op)
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await init_db(db)
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# Verify schema version is unchanged
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async with db.execute(
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"SELECT MAX(version) FROM schema_migrations;"
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) as cursor:
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row2 = await cursor.fetchone()
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assert row1 == row2
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finally:
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await db.close()
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