alembic_env_config_offline_online_migration_modes.py

1from logging.config import fileConfig
2
3from sqlalchemy import engine_from_config
4from sqlalchemy import pool
5
6from alembic import context
7
8# this is the Alembic Config object, which provides access to the values within the .ini file in use.
9config = context.config
10
11# Interpret the config file for Python logging.
12# This line sets up loggers basically.
13if config.config_file_name is not None:
14    fileConfig(config.config_file_name)
15
16# add your model's MetaData object here for 'autogenerate' support
17# from myapp import mymodel
18# target_metadata = mymodel.Base.metadata
19target_metadata = None
20
21# other values from the config, defined by the needs of env.py,
22# can be acquired:
23# my_important_option = config.get_main_option("my_important_option")
24# ... etc.
25
26
27def run_migrations_offline() -> None:
28    """Run migrations in 'offline' mode.
29
30    This configures the context with just a URL and not an Engine, 
31    though an Engine is also acceptable here. By skipping the Engine creation 
32    we don't even need a DBAPI to be available.
33
34    Calls to context.execute() here emit the given string to the script output.
35    """
36    url = config.get_main_option("sqlalchemy.url")
37    context.configure(
38        url=url,
39        target_metadata=target_metadata,
40        literal_binds=True,
41        dialect_opts={"paramstyle": "named"},
42    )
43
44    with context.begin_transaction():
45        context.run_migrations()
46
47
48def run_migrations_online() -> None:
49    """Run migrations in 'online' mode.
50
51    In this scenario we need to create an Engine and associate a connection 
52    with the context.
53    """
54    connectable = engine_from_config(
55        config.get_section(config.config_ini_section, {}),
56        prefix="sqlalchemy.",
57        poolclass=pool.NullPool,
58    )
59
60    with connectable.connect() as connection:
61        context.configure(
62            connection=connection, target_metadata=target_metadata
63        )
64
65        with context.begin_transaction():
66            context.run_migrations()
67
68
69if context.is_offline_mode():
70    run_migrations_offline()
71else:
72    run_migrations_online()