matrix-alertbot/my_project_name/storage.py

import logging

# The latest migration version of the database.
#
# Database migrations are applied starting from the number specified in the database's
# `migration_version` table + 1 (or from 0 if this table does not yet exist) up until
# the version specified here.
#
# When a migration is performed, the `migration_version` table should be incremented.
latest_migration_version = 0

logger = logging.getLogger(__name__)


class Storage(object):
    def __init__(self, database_config):
        """Setup the database

        Runs an initial setup or migrations depending on whether a database file has already
        been created

        Args:
            database_config: a dictionary containing the following keys:
                * type: A string, one of "sqlite" or "postgres"
                * connection_string: A string, featuring a connection string that
                    be fed to each respective db library's `connect` method
        """
        self.conn = self._get_database_connection(
            database_config["type"], database_config["connection_string"]
        )
        self.cursor = self.conn.cursor()
        self.db_type = database_config["type"]

        # Try to check the current migration version
        migration_level = 0
        try:
            self._execute("SELECT version FROM migration_version")
            row = self.cursor.fetchone()
            migration_level = row[0]
        except Exception:
            self._initial_setup()
        finally:
            if migration_level < latest_migration_version:
                self._run_migrations(migration_level)

        logger.info(f"Database initialization of type '{self.db_type}' complete")

    def _get_database_connection(self, database_type: str, connection_string: str):
        if database_type == "sqlite":
            import sqlite3

            # Initialize a connection to the database, with autocommit on
            return sqlite3.connect(connection_string, isolation_level=None)
        elif database_type == "postgres":
            import psycopg2

            conn = psycopg2.connect(connection_string)

            # Autocommit on
            conn.set_isolation_level(0)

            return conn

    def _initial_setup(self):
        """Initial setup of the database"""
        logger.info("Performing initial database setup...")

        # Set up the migration_version table
        self._execute(
            """
            CREATE TABLE migration_version (
                version INTEGER PRIMARY KEY
            )
        """
        )

        # Initially set the migration version to 0
        self._execute(
            """
            INSERT INTO migration_version (
                version
            ) VALUES (?)
        """,
            (0,),
        )

        # Set up any other necessary database tables here

        logger.info("Database setup complete")

    def _run_migrations(self, current_migration_version: int):
        """Execute database migrations. Migrates the database to the
        `latest_migration_version`

        Args:
            current_migration_version: The migration version that the database is
                currently at
        """
        logger.debug("Checking for necessary database migrations...")

        # if current_migration_version < 1:
        #    logger.info("Migrating the database from v0 to v1...")
        #
        #    # Add new table, delete old ones, etc.
        #
        #    # Update the stored migration version
        #    self._execute("UPDATE migration_version SET version = 1")
        #
        #    logger.info("Database migrated to v1")

    def _execute(self, *args):
        """A wrapper around cursor.execute that transforms placeholder ?'s to %s for postgres"""
        if self.db_type == "postgres":
            self.cursor.execute(args[0].replace("?", "%s"), *args[1:])
        else:
            self.cursor.execute(*args)