SqlAlchemy ForeignKey on different schema not found

Question

So have 2 different models on 2 different schemas. One has a foreign key relation to the other. I run BaseOne.metadata.create_all(engine) then BaseTwo.metadata.create_all(engine) I get sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column...

BaseOne = declarative_base(metadata=MetaData(schema="a"))
BaseTwo = declarative_base(metadata=MetaData(schema="b"))

class Parent(BaseOne):
    __tablename__ = "parent"
    parent_id = Column(Integer, primary_key=True)
    other_col = Column(String(20))
    children = relationship("Child", backref="parent")

class Child(BaseTwo):
    __tablename__ = "child"
    child_id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey("a.parent.parent_id"), nullable=False)

# Where I'm creating them
BaseOne.metadata.create_all(engine)
BaseTwo.metadata.create_all(engine)

Should note I've also tried explicitly stating the schema via __table_args__ . Also I have connected to my postgres instance and have verified that the parent table exists with the target column.

Answer 1

It appears the issue was due to the fact I used multiple MetaData objects. It appears that they were unable to see each other. Simplified to a single declarative base and using __table_args__ to declare the schemas appeared to work. If someone knows how to declare multiple metadata objects and still be able to use .create_all feel free to post.

Answer 2

This may be solved by using Alembic to manage table creation. Ensure that all bases are included in the target_metadata list eg:

# pylint: skip-file
import os
from logging.config import fileConfig

from alembic import context
from sqlalchemy import engine_from_config
from sqlalchemy import pool

import unimatrix.ext.octet.orm
import gpo.infra.orm


# this is the Alembic Config object, which provides
# access to the values within the .ini file in use.
config = context.config

# Interpret the config file for Python logging.
# This line sets up loggers basically.
fileConfig(config.config_file_name)

# add your model's MetaData object here
# for 'autogenerate' support
# from myapp import mymodel
# target_metadata = mymodel.Base.metadata
target_metadata = [
    unimatrix.ext.octet.orm.metadata,
    gpo.infra.orm.Relation.metadata
]


# Configure SQLAlchemy to use the DB_URI environment variable.
config.set_main_option("sqlalchemy.url", os.environ["DB_URI"])


def run_migrations_offline():
    """Run migrations in 'offline' mode.

    This configures the context with just a URL
    and not an Engine, though an Engine is acceptable
    here as well.  By skipping the Engine creation
    we don't even need a DBAPI to be available.

    Calls to context.execute() here emit the given string to the
    script output.

    """
    url = config.get_main_option("sqlalchemy.url")
    context.configure(
        url=url,
        target_metadata=target_metadata,
        literal_binds=True,
        dialect_opts={"paramstyle": "named"},
    )

    with context.begin_transaction():
        context.run_migrations()


def run_migrations_online():
    """Run migrations in 'online' mode.

    In this scenario we need to create an Engine
    and associate a connection with the context.

    """
    connectable = engine_from_config(
        config.get_section(config.config_ini_section),
        prefix="sqlalchemy.",
        poolclass=pool.NullPool,
    )

    with connectable.connect() as connection:
        context.configure(
            connection=connection, target_metadata=target_metadata
        )

        with context.begin_transaction():
            context.run_migrations()


if context.is_offline_mode():
    run_migrations_offline()
else:
    run_migrations_online()

``