Why did I have problems with alembic migrations

问题

Project structue(only directory with DB migrations):

--db_manage:
  alembic.ini
  --alembic:
    env.py
    script.py.mako
    README
    --versions:
      #migration files

When I try to run command: python db_manage/alembic/env.py, I have response like:

Traceback (most recent call last):
  File "db_manage/alembic/env.py", line 8, in <module>
    config = context.config
AttributeError: module 'alembic.context' has no attribute 'config'

In which case I have that problem?
P.S.
File alembic.ini:

# A generic, single database configuration.

[alembic]
# path to migration scripts
script_location = alembic

# template used to generate migration files
# file_template = %%(rev)s_%%(slug)s

# max length of characters to apply to the
# "slug" field
#truncate_slug_length = 40

# set to 'true' to run the environment during
# the 'revision' command, regardless of autogenerate
# revision_environment = false

# set to 'true' to allow .pyc and .pyo files without
# a source .py file to be detected as revisions in the
# versions/ directory
# sourceless = false

# version location specification; this defaults
# to numus/versions.  When using multiple version
# directories, initial revisions must be specified with --version-path
# version_locations = %(here)s/bar %(here)s/bat numus/versions

# the output encoding used when revision files
# are written from script.py.mako
# output_encoding = utf-8

sqlalchemy.url = postgresql://test:oe50yxXOspYDsaXSO7Gf@localhost/test


# Logging configuration
[loggers]
keys = root,sqlalchemy,alembic

[handlers]
keys = console

[formatters]
keys = generic

[logger_root]
level = WARN
handlers = console
qualname =

[logger_sqlalchemy]
level = WARN
handlers =
qualname = sqlalchemy.engine

[logger_alembic]
level = INFO
handlers =
qualname = alembic

[handler_console]
class = StreamHandler
args = (sys.stderr,)
level = NOTSET
formatter = generic

[formatter_generic]
format = %(levelname)-5.5s [%(name)s] %(message)s
datefmt = %H:%M:%S

File env.py:

from __future__ import with_statement
from alembic import context
from sqlalchemy import engine_from_config, pool
from logging.config import fileConfig

# 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.
fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = None

# other values from the config, defined by the needs of env.py,
# can be acquired:
# my_important_option = config.get_main_option("my_important_option")
# ... etc.


def run_migrations_offline():
    """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.

    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url, target_metadata=target_metadata, literal_binds=True)

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix='sqlalchemy.',
        poolclass=pool.NullPool)

    with connectable.connect() as connection:
        context.configure(
            connection=connection,
            target_metadata=target_metadata
        )

        with context.begin_transaction():
            context.run_migrations()

if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

回答1:

There are 2 things wrong in the way you try to invoke the migration tool. Firstly, you should use the alembic script instead of trying to run the env.py directly. From the tutorial:

env.py - This is a Python script that is run whenever the alembic migration tool is invoked. At the very least, it contains instructions to configure and generate a SQLAlchemy engine, procure a connection from that engine along with a transaction, and then invoke the migration engine, using the connection as a source of database connectivity.

Secondly, though you can keep your alembic.ini wherever, the default behaviour is to look in the current directory:

Alembic placed a file alembic.ini into the current directory. This is a file that the alembic script looks for when invoked. This file can be anywhere, either in the same directory from which the alembic script will normally be invoked, or if in a different directory, can be specified by using the --config option to the alembic runner.

So if it is held somewhere else, you must instruct alembic about the location using the -c, or --config, switch. For example:

alembic --config db_manage/alembic.ini

来源：https://stackoverflow.com/questions/46050187/why-did-i-have-problems-with-alembic-migrations