Alembic migrations when some tables exists

Question

I have some migrations in alembic, and try to run alembic upgrade head to up-to-date my DB for revision, but in some cases I have tables, which already exists, so I have an error:

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']

How can I ignore existing tables?
That means something like: if table exist - continue but not abort

Answer 1

You need to go to your migration/version folder or alembic :

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

and edit the last migration script by removing the script for creating the table in the upgrade function and remove the reverse task in downgrade function in the same script.

As said in flask migrate :

The migration script needs to be reviewed and edited

And I quote this from alembic:

We review and modify these by hand as needed, then proceed normally.

Edit :

You can also do that automatically by using the include_object as suggested by this answer