can't run "flask db history" , fails with get_bind error

[jamadriz]

Hi all, any help appreciated.
I have Flask-Migrate version 4.0.5 installed, and Flask = "^2.3.0".
Migration commands work as expected (upgrade, downgrade)
However, when trying to run flask db history to fix a conflict, I get this error trace:

  File "<frozen importlib._bootstrap_external>", line 850, in exec_module
  File "<frozen importlib._bootstrap>", line 228, in _call_with_frames_removed
  File "[...]/backend/migrations/versions/f453c62def1d_metadatas_markdown_to_html.py", line 20, in <module>
    bind = op.get_bind()
  File "<string>", line 7, in get_bind
  File "[...]/Library/Caches/pypoetry/virtualenvs/[...]-CrRdXKkv-py3.9/lib/python3.9/site-packages/alembic/util/langhelpers.py", line 136, in _name_error
    raise NameError(
NameError: Can't invoke function 'get_bind', as the proxy object has not yet been established for the Alembic 'Operations' class.  Try placing this code inside a callable.

any light?

Thanks!

[miguelgrinberg]

Your env.py file in the migrations directory is probably too old. If you have not made custom changes to this file, I would just take a copy of the file from here and replace it.

[jamadriz]

Thanks for the quick reply, getting same error after replacing the env.py

[jamadriz]

Update, after updating the env.py and also the Flask-SQLAlchemy version to > 3, I get a different error:

  File "[...]/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/attributes.py", line 2620, in register_attribute_impl
    impl = cast("Type[WriteOnlyAttributeImpl]", impl_class)(
  File "[...]/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/attributes.py", line 1217, in __init__
    super().__init__(*arg, **kw)
TypeError: __init__() missing 1 required positional argument: 'dispatch'

[jamadriz]

FLASK_ENV=development FLASK_APP=src/backend/api.py poetry run flask db history
Traceback (most recent call last):
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/bin/flask", line 8, in <module>
    sys.exit(main())
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask/cli.py", line 1107, in main
    cli.main()
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/click/core.py", line 1078, in main
    rv = self.invoke(ctx)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/click/core.py", line 1682, in invoke
    cmd_name, cmd, args = self.resolve_command(ctx, args)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/click/core.py", line 1729, in resolve_command
    cmd = self.get_command(ctx, cmd_name)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask/cli.py", line 613, in get_command
    app = info.load_app()
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask/cli.py", line 337, in load_app
    app = locate_app(import_name, name)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask/cli.py", line 247, in locate_app
__import__(module_name)
[...]
  File "/Users/acme/AcmeCorp/backend/src/backend/db/__init__.py", line 9, in <module>
    from .comment import Comment
  File "/Users/acme/AcmeCorp/backend/src/backend/db/comment.py", line 30, in <module>
    class Comment(db.Model, Serializer):
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask_sqlalchemy/model.py", line 92, in __init__
    super().__init__(name, bases, d, **kwargs)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask_sqlalchemy/model.py", line 144, in __init__
    super().__init__(name, bases, d, **kwargs)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/decl_api.py", line 196, in __init__
    _as_declarative(reg, cls, dict_)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py", line 247, in _as_declarative
    return _MapperConfig.setup_mapping(registry, cls, dict_, None, {})
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py", line 328, in setup_mapping
    return _ClassScanMapperConfig(
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py", line 582, in __init__
    self._early_mapping(mapper_kw)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py", line 369, in _early_mapping
    self.map(mapper_kw)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/decl_base.py", line 1957, in map
    mapper_cls(self.cls, self.local_table, **self.mapper_args),
  File "<string>", line 2, in __init__
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/util/deprecations.py", line 281, in warned
    return fn(*args, **kwargs)  # type: ignore[no-any-return]
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/mapper.py", line 851, in __init__
    self._configure_properties()
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/mapper.py", line 1748, in _configure_properties
    self._configure_property(
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/mapper.py", line 2230, in _configure_property
    prop.instrument_class(self)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy_utils/generic.py", line 173, in instrument_class
    attributes.register_attribute(
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/attributes.py", line 2588, in register_attribute
    register_attribute_impl(class_, key, **kw)
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/attributes.py", line 2620, in register_attribute_impl
    impl = cast("Type[WriteOnlyAttributeImpl]", impl_class)(
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/sqlalchemy/orm/attributes.py", line 1217, in __init__
    super().__init__(*arg, **kw)
TypeError: __init__() missing 1 required positional argument: 'dispatch'
acme@mac backend % ```

[miguelgrinberg]

I don't have a definitive answer, but looking at the SQLAlchemy code there has been a recent change in the area where this error occurs (commit). This change appeared in version 2.0.22. If you are using a version that is older, try upgrading. Or if you are on this one or a newer version, then try a downgrade to 2.0.21. I think what might be happening is that another package (possibly Flask-SQLAlchemy) is affected by the change in this commit.

[jamadriz]

I downgraded to 2.0.21, and indeed getting a different behaviour. Now I get a problem with a column definition which works in previous 1.4 version:

class Image(db.Model, Serializer):
   [...]
    metadata_ = db.Column("metadata", get_json_type())

where

def get_json_type():
    if db.app is None:
        return JSON

    with db.app.app_context():
        if db.engine.dialect.name == "sqlite":
            return JSON
        else:
            return JSONB

the error seems to be with the db.app reference in the column type definition.

  File "/Users/acme/AcmeCorp/backend/src/backend/db/image.py", line 51, in Image
    metadata_ = db.Column("metadata", get_json_type())
  File "/Users/acme/AcmeCorp/backend/src/backend/db/image.py", line 29, in get_json_type
    if db.app is None:
  File "/Users/acme/Library/Caches/pypoetry/virtualenvs/backend-CrRdXKkv-py3.9/lib/python3.9/site-packages/flask_sqlalchemy/extension.py", line 1008, in __getattr__
    raise AttributeError(name)
AttributeError: app

seems strange to me that 1.4 doesn't complain about this.

[miguelgrinberg]

That db.app looks wrong to me. Not a good pattern to access private members of the db object. This is something from Flask-SQLAlchemy that they likely removed in recent versions. You are going to need to import your app instance if you need to keep doing this. Probably better to find a different way to handle this, though, like maybe an environment variable. Anything that does not require the app instance would be better here.

[jamadriz]

Makes sense, thanks Miguel, really appreciate your help. I will keep digging in the dispatch error on latest SQLAlchemy release, will post here any findings.