Name error when using a custom type imported from another file.

[0x1618]

Describe the bug
When running db migrate after db upgrade, an name error occurs if a custom type is imported from another file because Alembic does not handle the import. It's important to use the Flask-adapted version, but I think this issue is more related to Alembic itself.

Expected behavior
I expected Alembic to auto-import the required type.

To Reproduce
Use a custom type that is in another file, then import it into the model and run upgrade and migrate.

"""empty message

Revision ID: abd06113edc0
Revises: 4d3e79e25c52
Create Date: 2024-08-07 02:04:27.676951

"""
from alembic import op
import sqlalchemy as sa
from sqlalchemy.dialects import mysql

# revision identifiers, used by Alembic.
revision = 'abd06113edc0'
down_revision = '4d3e79e25c52'
branch_labels = None
depends_on = None


def upgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    with op.batch_alter_table('encryption_keys', schema=None) as batch_op:
        batch_op.alter_column('encrypted_key',
               existing_type=mysql.VARCHAR(length=94),
               type_=resources.db_models.custom_types.app_master_key_encrypted.AppMasterKeyEncrypted(length=95),
               existing_nullable=False)

    # ### end Alembic commands ###


def downgrade():
    # ### commands auto generated by Alembic - please adjust! ###
    with op.batch_alter_table('encryption_keys', schema=None) as batch_op:
        batch_op.alter_column('encrypted_key',
               existing_type=resources.db_models.custom_types.app_master_key_encrypted.AppMasterKeyEncrypted(length=95),
               type_=mysql.VARCHAR(length=94),
               existing_nullable=False)

    # ### end Alembic commands ###

from resources.db_models.custom_types.app_master_key_encrypted import \
    AppMasterKeyEncrypted


class EncryptionKeyModel(db.Model):
    __tablename__ = 'encryption_keys'

    uuid = db.Column(db.String(36), primary_key=True)
    encrypted_key = db.Column(AppMasterKeyEncrypted(94), nullable=False)

Error

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File ".venv\Lib\site-packages\flask\__main__.py", line 3, in <module>
    main()
  File ".venv\Lib\site-packages\flask\cli.py", line 1105, in main
    cli.main()
  File ".venv\Lib\site-packages\click\core.py", line 1078, in main
    rv = self.invoke(ctx)
         ^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\click\core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\click\core.py", line 1688, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\click\core.py", line 1434, in invoke
    return ctx.invoke(self.callback, **ctx.params)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\click\core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\click\decorators.py", line 33, in new_func
    return f(get_current_context(), *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\flask\cli.py", line 386, in decorator
    return ctx.invoke(f, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\click\core.py", line 783, in invoke
    return __callback(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\flask_migrate\cli.py", line 154, in upgrade
    _upgrade(directory, revision, sql, tag, x_arg)
  File ".venv\Lib\site-packages\flask_migrate\__init__.py", line 111, in wrapped
    f(*args, **kwargs)
  File ".venv\Lib\site-packages\flask_migrate\__init__.py", line 200, in upgrade
    command.upgrade(config, revision, sql=sql, tag=tag)
  File ".venv\Lib\site-packages\alembic\command.py", line 406, in upgrade
    script.run_env()
  File ".venv\Lib\site-packages\alembic\script\base.py", line 582, in run_env
    util.load_python_file(self.dir, "env.py")
  File ".venv\Lib\site-packages\alembic\util\pyfiles.py", line 95, in load_python_file
    module = load_module_py(module_id, path)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File ".venv\Lib\site-packages\alembic\util\pyfiles.py", line 113, in load_module_py
    spec.loader.exec_module(module)  # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<frozen importlib._bootstrap_external>", line 995, in exec_module
  File "<frozen importlib._bootstrap>", line 488, in _call_with_frames_removed
  File "migrations\env.py", line 113, in <module>
    run_migrations_online()
  File "migrations\env.py", line 107, in run_migrations_online
    context.run_migrations()
  File "<string>", line 8, in run_migrations
  File ".venv\Lib\site-packages\alembic\runtime\environment.py", line 946, in run_migrations
    self.get_context().run_migrations(**kw)
  File ".venv\Lib\site-packages\alembic\runtime\migration.py", line 628, in run_migrations
    step.migration_fn(**kw)
  File "migrations\versions\5ed08815988d_.py", line 24, in upgrade
    type_=resources.db_models.custom_types.app_master_key_encrypted.AppMasterKeyEncrypted(length=96),
          ^^^^^^^^^
NameError: name 'resources' is not defined

Versions.

• OS: Win 11.
• Python: 3.12
• Alembic: 1.13.2
• SQLAlchemy: 1.4.53
• Database: MySQL.
• DBAPI: I'm sorry but i don't know.

[zzzeek]

hi -

check out the docs at https://alembic.sqlalchemy.org/en/latest/autogenerate.html#controlling-the-module-prefix. you want to add the imports you need for all your custom types to script.py.mako and then set user_module_prefix appropriately