InvalidRequestError: Table … is already defined for this MetaData instance (table inheritance on v2.2) #478
Description
On Flask-SQLAlchemy 2.2 (Flask 0.12, SQLAlchemy 1.1.6, Python 3.5.3) I the following traceback that does not occur with Flask-SQLAlchemy 2.1:
Traceback (most recent call last):
File "application.py", line 19, in <module>
class ChildA(Parent):
File "/home/user/project/venv/lib/python3.5/site-packages/flask_sqlalchemy/__init__.py", line 602, in __init__
DeclarativeMeta.__init__(self, name, bases, d)
File "/home/user/project/venv/lib/python3.5/site-packages/sqlalchemy/ext/declarative/api.py", line 64, in __init__
_as_declarative(cls, classname, cls.__dict__)
File "/home/user/project/venv/lib/python3.5/site-packages/sqlalchemy/ext/declarative/base.py", line 88, in _as_declarative
_MapperConfig.setup_mapping(cls, classname, dict_)
File "/home/user/project/venv/lib/python3.5/site-packages/sqlalchemy/ext/declarative/base.py", line 103, in setup_mapping
cfg_cls(cls_, classname, dict_)
File "/home/user/project/venv/lib/python3.5/site-packages/sqlalchemy/ext/declarative/base.py", line 131, in __init__
self._setup_table()
File "/home/user/project/venv/lib/python3.5/site-packages/sqlalchemy/ext/declarative/base.py", line 395, in _setup_table
**table_kw)
File "/home/user/project/venv/lib/python3.5/site-packages/sqlalchemy/sql/schema.py", line 418, in __new__
"existing Table object." % key)
sqlalchemy.exc.InvalidRequestError: Table 'items' is already defined for this MetaData instance. Specify 'extend_existing=True' to redefine options and columns on an existing Table object.Somewhat minimal code to reproduce:
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
class Parent(db.Model):
__tablename__ = 'items'
__mapper_args__ = {
'polymorphic_identity': 'parent',
'polymorphic_on': 'type',
}
id = db.Column(db.Integer, primary_key=True)
type = db.Column(db.Unicode(10), nullable=False)
class ChildA(Parent):
__mapper_args__ = {
'polymorphic_identity': 'child_a',
}
foo = db.Column(db.Integer)
class ChildB(Parent):
__mapper_args__ = {
'polymorphic_identity': 'child_b',
}
bar = db.Column(db.Integer)
app = Flask(__name__)
app.run()Unless I've been doing that wrong the whole time and just got away with it by chance, I think this might be unintended behavior on Flask-SQLAlchemy's side.