SQLAlchemy: AttributeError: 'Table' object has no attribute 'id'

Question

I'm building a DB, that matches my local product catalogue with foreign ones. When I had the only table 'Catalog' SQLAlchemy worked fine. After adding tables Competitors and Competitors_catalog all my attempts to add records to both new tables returned with error.

AttributeError: 'Table' object has no attribute 'id'

I change/remove/play with relationship between Competitors and Competitors_catalog several times, drop and create tables through flask-migrate back and forth, but keep receiving same error. Simple query like Competitors.query.all() returns the same. Removed db.relationship() - same result. Then I finally rolled back to a clear db and initiated it with flask-migrate from scratch. After that I begin to receive same error trying to add records to Catalog table, which worked fine before I rolled back. Which is odd since I made no changes to that part of the code.

class Catalog(db.Model):
    __tablename__ = 'catalog'

    id            = db.Column(db.Integer, primary_key=True)
    name          = db.Column(db.String(60), index=True, nullable=False)
    parent_id     = db.Column(db.Integer, db.ForeignKey('catalog.id'), default=None)
    url           = db.Column(db.String())
    created       = db.Column(db.DateTime, default=datetime.now())
    last_modified = db.Column(db.DateTime, index=True, onupdate=datetime.now())

    categories = db.relationship('Catalog', remote_side='catalog.id', backref='parent')

class Competitors(db.Model):
    __tablename__ = 'competitors'

    id            = db.Column(db.Integer, primary_key=True)
    name          = db.Column(db.String(40), index=True, nullable=False)
    base_url      = db.Column(db.String())
    cat_url       = db.Column(db.String())
    created       = db.Column(db.DateTime, default=datetime.now())
    last_modified = db.Column(db.DateTime, onupdate=datetime.now(), default=datetime.now())

    sells = db.relationship('Competitors_catalog', backref='competitor', cascade="all, delete-orphan", passive_deletes=True, lazy='dynamic')

class CompCatalog(db.Model):
    __tablename__ = 'compcatalog'

    id            = db.Column(db.Integer, primary_key=True)
    out_id        = db.Column(db.Integer)
    name          = db.Column(db.String(60), index=True, nullable=False)
    top_section   = db.Column(db.Integer, default=None)
    comp_id       = db.Column(db.Integer, db.ForeignKey('competitors.id', ondelete="CASCADE"))
    url           = db.Column(db.String())
    created       = db.Column(db.DateTime, default=datetime.now())
    last_modified = db.Column(db.DateTime, index=True, onupdate=datetime.now())

Simple creation of new instance returns error. But worked fine before roll back.

from .models import Catalog

name = 'Apple'
rec = Catalog(name=name)

Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File ".../app/helpers.py", line 31, in create_catalog
    rec = Catalog(name=name)
  File "<string>", line 2, in __init__
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/instrumentation.py", line 376, in _new_state_if_none
    state = self._state_constructor(instance, self)
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/util/langhelpers.py", line 855, in __get__
    obj.__dict__[self.__name__] = result = self.fget(obj)
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/instrumentation.py", line 202, in _state_constructor
    self.dispatch.first_init(self, self.class_)
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/event/attr.py", line 322, in __call__
    fn(*args, **kw)
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/mapper.py", line 3360, in _event_on_first_init
    configure_mappers()
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/mapper.py", line 3248, in configure_mappers
    mapper._post_configure_properties()
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/mapper.py", line 1947, in _post_configure_properties
    prop.init()
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/interfaces.py", line 196, in init
    self.do_init()
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/relationships.py", line 1860, in do_init
    self._process_dependent_arguments()
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/orm/relationships.py", line 1889, in _process_dependent_arguments
    setattr(self, attr, attr_value())
  File ".../.virtualenvs/.../lib/python3.6/site-packages/sqlalchemy/ext/declarative/clsregistry.py", line 294, in __call__
    x = eval(self.arg, globals(), self._dict)
  File "<string>", line 1, in <module>
AttributeError: 'Table' object has no attribute 'id'

Ilja Everilä · Accepted Answer · 2019-09-12 10:46:44Z

2

The remote_side argument can be passed as an evaluable string, which you've done:

remote_side='catalog.id'

The problem is that the namespace it is evaluated in contains the Table objects and the model classes, and you're referencing a Table instead of the model class. Just alter the remote side to

remote_side='Catalog.id'

or just pass the id column in the class body directly:

class Catalog(db.Model):
    __tablename__ = 'catalog'

    id            = db.Column(db.Integer, primary_key=True)
    ...
    categories = db.relationship('Catalog', remote_side=id, backref='parent')

answered Sep 12, 2019 at 10:46

Ilja Everilä

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6 Comments

Evgeny Over a year ago

Do you have any ideas why this relationship brings the same error? comp_id = db.Column(db.Integer, db.ForeignKey('competitors.id', ondelete="CASCADE"))

Ilja Everilä Over a year ago

Hmm, at a glance no. ForeignKey is different from a relationship in that it works at the DB level and so should use the <table_name>.<column_key> notation: docs.sqlalchemy.org/en/13/core/…

Evgeny Over a year ago

Yes, in pure SQLAlchemy it works that way. I use flask-sqlalchemy, they suggest to address through __tablename__. Thank you for the answer.

Ilja Everilä Over a year ago

Flask-SQLA is basically SQLA — with Flask integrations, a few tweaks, and a customized Session. Where can the suggestion to use __tablename__ be found? It'd br interesting to see what's it like.

Evgeny Over a year ago

As I understand the issue, SQLA working with Postgre converts camelcase class name to a name divided with underscores, e.g. class CompetitorsCatalog to competitors_catalog, while I was addressing to competitorscatalog. That solves the issue for me.

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