I've found that if __table_args__ is present on a child class in a single-table
inheritance setup
<http://docs.sqlalchemy.org/en/latest/orm/inheritance.html#single-table-inheritance>,
SQLAlchemy throws sqlalchemy.exc.ArgumentError: Can't place __table_args__
on an inherited class with no table. At the same time it is possible to
define a column with index=True on a child class, which alters the parent
table the same way as __table_args__.
Here is my setup:
import sqlalchemy as sa
import sqlalchemy.ext.declarative
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class A(Base):
__tablename__ = 'a'
id = sa.Column(sa.Integer, primary_key=True)
type = sa.Column(sa.Text, nullable=False)
__mapper_args__ = {
'polymorphic_on': type,
}
class B(A):
b = sa.Column(sa.Integer, index=True)
__mapper_args__ = {
'polymorphic_identity': 'b',
}
class C(A):
c = sa.Column(sa.Integer)
__mapper_args__ = {
'polymorphic_identity': 'c',
}
__table_args__ = (
sa.Index('ix_test', c),
)
engine = sa.engine.create_engine("sqlite://", echo=True)
Base.metadata.create_all(engine)
session = sa.orm.Session(engine)
session.add_all([
B()
])
session.commit()
print(session.query(A))
And it throws:
Traceback (most recent call last):
File "test.py", line 29, in <module>
class C(A):
File
"/home/andrei/projects/my_project/.tox/dev/lib/python3.5/site-packages/sqlalchemy/ext/decla
rative/api.py", line 64, in __init__
_as_declarative(cls, classname, cls.__dict__)
File
"/home/andrei/projects/my_project/.tox/dev/lib/python3.5/site-packages/sqlalchemy/ext/decla
rative/base.py", line 88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File
"/home/andrei/projects/my_project/.tox/dev/lib/python3.5/site-packages/sqlalchemy/ext/decla
rative/base.py", line 103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File
"/home/andrei/projects/my_project/.tox/dev/lib/python3.5/site-packages/sqlalchemy/ext/decla
rative/base.py", line 133, in __init__
self._setup_inheritance()
File
"/home/andrei/projects/my_project/.tox/dev/lib/python3.5/site-packages/sqlalchemy/ext/decla
rative/base.py", line 442, in _setup_inheritance
"Can't place __table_args__ on an inherited class "
sqlalchemy.exc.ArgumentError: Can't place __table_args__ on an inherited
class with no table.
Do somebody know any workarounds?
--
SQLAlchemy -
The Python SQL Toolkit and Object Relational Mapper
http://www.sqlalchemy.org/
To post example code, please provide an MCVE: Minimal, Complete, and Verifiable
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