当某些表存在时进行 Alembic 迁移

Question

我在 alembic 中有一些迁移，并尝试运行alembic upgrade head最新的数据库进行修订，但在某些情况下，我有已经存在的表，所以我有一个错误：

alembic upgrade head
INFO  [alembic.runtime.migration] Context impl PostgresqlImpl.
INFO  [alembic.runtime.migration] Will assume transactional DDL.
INFO  [alembic.runtime.migration] Running upgrade  -> 3137cf88d8c6, create tables
Traceback (most recent call last):
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1182, in _execute_context
    context)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/default.py", line 470, in do_execute
    cursor.execute(statement, parameters)
psycopg2.ProgrammingError: relation "City" already exists


The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/home/toweya/.virtualenvs/numus3/bin/alembic", line 11, in <module>
    sys.exit(main())
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/config.py", line 479, in main
    CommandLine(prog=prog).main(argv=argv)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/config.py", line 473, in main
    self.run_cmd(cfg, options)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/config.py", line 456, in run_cmd
    **dict((k, getattr(options, k, None)) for k in kwarg)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/command.py", line 254, in upgrade
    script.run_env()
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/script/base.py", line 416, in run_env
    util.load_python_file(self.dir, 'env.py')
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/util/pyfiles.py", line 93, in load_python_file
    module = load_module_py(module_id, path)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/util/compat.py", line 64, in load_module_py
    module_id, path).load_module(module_id)
  File "<frozen importlib._bootstrap_external>", line 388, in _check_name_wrapper
  File "<frozen importlib._bootstrap_external>", line 809, in load_module
  File "<frozen importlib._bootstrap_external>", line 668, in load_module
  File "<frozen importlib._bootstrap>", line 268, in _load_module_shim
  File "<frozen importlib._bootstrap>", line 693, in _load
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 665, in exec_module
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "numus/env.py", line 68, in <module>
    run_migrations_online()
  File "numus/env.py", line 63, in run_migrations_online
    context.run_migrations()
  File "<string>", line 8, in run_migrations
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/runtime/environment.py", line 817, in run_migrations
    self.get_context().run_migrations(**kw)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/runtime/migration.py", line 323, in run_migrations
    step.migration_fn(**kw)
  File "/home/toweya/PycharmProjects/NumusPortal/portal/db_manage/numus/versions/3137cf88d8c6_create_tables.py", line 30, in upgrade
    sa.Column('name', sa.String(64), nullable=False),
  File "<string>", line 8, in create_table
  File "<string>", line 3, in create_table
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/operations/ops.py", line 1106, in create_table
    return operations.invoke(op)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/operations/base.py", line 318, in invoke
    return fn(self, operation)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/operations/toimpl.py", line 101, in create_table
    operations.impl.create_table(table)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/ddl/impl.py", line 194, in create_table
    self._exec(schema.CreateTable(table))
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/alembic/ddl/impl.py", line 118, in _exec
    return conn.execute(construct, *multiparams, **params)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 945, in execute
    return meth(self, multiparams, params)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/sql/ddl.py", line 68, in _execute_on_connection
    return connection._execute_ddl(self, multiparams, params)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1002, in _execute_ddl
    compiled
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1189, in _execute_context
    context)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1393, in _handle_dbapi_exception
    exc_info
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/util/compat.py", line 203, in raise_from_cause
    reraise(type(exception), exception, tb=exc_tb, cause=cause)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/util/compat.py", line 186, in reraise
    raise value.with_traceback(tb)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/base.py", line 1182, in _execute_context
    context)
  File "/home/toweya/.virtualenvs/numus3/lib/python3.5/site-packages/sqlalchemy/engine/default.py", line 470, in do_execute
    cursor.execute(statement, parameters)
sqlalchemy.exc.ProgrammingError: (psycopg2.ProgrammingError) relation "City" already exists
 [SQL: '\nCREATE TABLE "City" (\n\tid SERIAL NOT NULL, \n\tgeoid INTEGER NOT NULL, \n\tname VARCHAR(64) NOT NULL, \n\tPRIMARY KEY (id), \n\tUNIQUE (geoid)\n)\n\n']

如何忽略现有表？
这意味着：如果表存在 - 继续但不中止

Answer 1

您需要转到迁移/版本文件夹或 alembic ：

/path/to/prooject/alembic/versions/3137cf88d8c6.py

编辑最后一个迁移脚本，删除升级功能中创建表的脚本，并删除同一脚本中降级功能中的反向任务。

正如烧瓶迁移中所述：

迁移脚本需要审核和编辑

我引用了alembic中的这段话：

我们根据需要手动审查和修改这些内容，然后正常进行。

编辑 ：

您也可以按照此答案include_object的建议自动执行此操作