Alembic Migrations on Multiple Models

Question

I am attempting to create a revision with --autogenerate using Alembic for two Models, but am receiving a duplicate table keys error. Does, a schema need to be specified? If so, how can it be set? The documentation I've read says to use __table_args__ = {'schema': 'somename'}, but that hasn't helped. Any tips or suggestions are greatly appreciated.

My current setup is:

base.py

from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()

workspace.py

from sqlalchemy import Column, Integer, String
from base import Base

class WorkspaceModel(Base):

    __tablename__ = 'workspaces'

    id = Column(Integer, primary_key=True)
    name = Column(String)

host.py

from sqlalchemy import Column, Integer, String
from base import Base

class HostModel(Base):

    __tablename__ = 'hosts'

    id = Column(Integer, primary_key=true)
    ip = Column(String)

alembic/env.py

from host import HostModel
from workspace import WorkspaceModel
target_metadata = [HostModel.metadata, WorkspaceModel.metadata]

Error

ValueError: Duplicate table keys across multiple MetaData objects: "hosts", "workspaces"

Answer 1

To make it clear from what @esdotzed and @univerio said, you have to use a single Base.metadata - but still import the individual models.

In the original question, this is how the alembic/env.py should look like:

from base import Base

# This two won't be referenced, but *have* to be imported to populate `Base.metadata`
from host import HostModel
from workspace import WorkspaceModel

target_metadata = Base.metadata

If you didn't import both models, the autogenerated migration would end up deleting your whole database - because Base.metadata doesn't know about any model by itself.

Answer 2

quoting univerio's answer from the comment section:

target_metadata should just be target_metadata = Base.metadata

Using Base.metadata doesn't mean you can remove the imports from host import HostModel and from workspace import WorkspaceModel

It worked for me.