Adding @declared_attr __tablename__ to Mixin is overridden by _BoundDeclarativeMeta

[mike-hart]

Using 2.0

I was using a mixin on my models to add a __tablename__ method to work out a prefixed/namespaced table name based on the class name but _BoundDeclarativeMeta's doesn't appear to check against base classes before adding its own.

This lead to errors like:
NoReferencedTableError: Foreign key associated with column 'not_yet_built.dependent_thoroughfare_id' could not find table 'paf_thoroughfare' with which to generate a foreign key to target column 'thoroughfare_id'

class PAFMixin(object):

    @declared_attr
    def __tablename__(cls):
        return 'paf' + re.sub(
            '[A-Z]', lambda match: '_' + match.group(0).lower(), cls.__name__)

Note that the class would prefix the table-name with paf, but this was not present in the first name of the exception (the latter is the reference from the ForeignKey itself). This prevents namespacing on systems that don't support schema (MySQL) and could be very confusing for others.

[davidism]

Would you produce a full test case for this? Also, ensure that you are using the latest version of SQLAlchemy 1.0, 0.9, or 0.8 branches, and specify which you're using.

[mike-hart]

import re

from flask import Flask
from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy import (Column, ForeignKey, Integer)
from sqlalchemy.ext.declarative import declared_attr


app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite://'
db = SQLAlchemy(app)


class PAFMixin(object):

    @declared_attr
    def __tablename__(cls):
        return 'paf' + re.sub(
            '[A-Z]', lambda match: '_' + match.group(0).lower(), cls.__name__)


class Locality(PAFMixin, db.Model):

    locality_id = Column(Integer, primary_key=True)


class Address(PAFMixin, db.Model):

    address_id = Column(Integer, primary_key=True)
    locality_id = Column(Integer, ForeignKey('paf_locality.locality_id'))


db.create_all()

Results in:
sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column 'address.locality_id' could not find table 'paf_locality' with which to generate a foreign key to target column 'locality_id'

$ pip freeze | grep Alc
Flask-SQLAlchemy==2.0
SQLAlchemy==1.0.6

Hopefully this is sufficient information?

[paxswill]

I also encountered this, and have a pair of test cases (909bb21)in my mixin-tablenames branch. The second commit (19fc6ab) resolves the test cases, but it feels like a really hacky solution.