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Posted 2013 Aug 07 15:18

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Posted 2013 Aug 07 15:17

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Posted 2013 Aug 07 03:33

SqlAlchemy Relationship Error: 'property of that name exists on mapper'

The Setup

I'm writing a web app in python with Flask and SqlAlchemy with MySQL.

[the solution(#fixed)

The Code

Starting with the following (slightly snipped for brevity) python/SqlAlchemy code in `

/markbox/models.py`:

class UserBlog(ModelBase):
    __tablename__ = 'user_blog'

    id = sa.Column(sa.Integer, primary_key=True)
    uid = sa.Column(strcol)
    # blog title
    name = sa.Column(strcol)

    # returns a query =&gt; blog.sync_stats.all()
    sync_stats = relationship(
        'models.SyncStats', backref='blog',
        lazy='dynamic')

class SyncStats(ModelBase):
    """
    Store various statistics about sync operations
    """
    __tablename__ = 'system_syncstats'

    id = sa.Column(sa.Integer, primary_key=True)
    uid = sa.Column(strcol, sa.ForeignKey('user_blogsettings.uid'))

And this code in <project>/markbox/tools/test.py:

import sys
import os

sys.path.append(os.path.abspath('.'))
sys.path.append(os.path.abspath('markbox'))
print sys.path

from markbox.models import UserBlog, SyncStats

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import Column, Integer, String, DateTime
from sqlalchemy.orm import sessionmaker

SQLALCHEMY_DATABASE_URI = "mysql://markbox_user:markbox@localhost/markbox"

engine = create_engine(SQLALCHEMY_DATABASE_URI, echo='debug')
Session = sessionmaker(bind=engine)
session = Session()

if __name__ == '__main__':
    blog = UserBlog.query.limit(1)

The Error

When run from the command line in <project>:

% python markbox/tools/test.py

I get:

['/Users/sivy/Projects/personal/markbox/markbox/tools', ..., '/Users/sivy/Projects/personal/markbox', '/Users/sivy/Projects/personal/markbox/markbox']
Traceback (most recent call last):
  File "markbox/tools/test.py", line 25, in <module>
    blog = UserBlog.query.limit(1)
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/scoping.py", line 131, in __get__
    mapper = class_mapper(owner)
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/util.py", line 1112, in class_mapper
    mapper = _inspect_mapped_class(class_, configure=configure)
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/util.py", line 1045, in _inspect_mapped_class
    mapperlib.configure_mappers()
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 2122, in configure_mappers
    mapper._post_configure_properties()
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/mapper.py", line 1244, in _post_configure_properties
    prop.init()
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/interfaces.py", line 231, in init
    self.do_init()
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/properties.py", line 1031, in do_init
    self._generate_backref()
  File "/Users/sivy/.virtualenvs/markbox/lib/python2.7/site-packages/sqlalchemy/orm/properties.py", line 1220, in _generate_backref
    self, m))
sqlalchemy.exc.ArgumentError: Error creating backref 'blog' on relationship 'UserBlog.sync_stats': property of that name exists on mapper 'Mapper|SyncStats|system_syncstats'

What I've Done

I've already confirmed that:

the SyncStats model has no "blog" property (it used to have a method, decorated with @property).
I've deleted any existing *.pyc files to make sure that the interpreter is not picking up pre-compiled code.

The solution

So, the problem turned out to be that the models were being imported from two paths:

from models import UserBlog

and later:

from markbox.models import UserBlog

This caused the intilization code to be run twice, and the resulting error.

Posted 2013 Aug 07 00:00

Z-index on a Glass browser should have a whole new meaning #css

Posted 2013 Aug 06 19:31

RT @scalzi: That's just mean. http://t.co/LQXMnucq2B

Posted 2013 Aug 06 17:44

Glory Box. So sublime #portishead

Posted 2013 Aug 06 17:43

@agiletortoise Welder is a definite MUST HAVE.

Posted 2013 Aug 06 17:26

RT @jasonbartz: The first step to writing a blog post is trying to remember how to use the blog software you wrote.

Posted 2013 Aug 06 15:35

So fed up with InnoDB issues (with Repeatable reads) that I'm installing Postgres. Cue #nowihavetwoproblems jokes.

Posted 2013 Aug 06 13:16

@pixel it truly works for anything.

Posted 2013 Aug 06 03:30

@pixel Yeah, saw that from a ways off.

Posted 2013 Aug 06 03:29

Man. Hot Italian Sausages and I officially do not get along.

Posted 2013 Aug 06 02:51

RT @HackerNewsOnion: 99% of programming is choosing a templating language and the rest is explaining your decision in a blog post.

Posted 2013 Aug 06 02:25

Crowning Moment of Heart Warming

My kids, wife, and Mom went to the movies today (Turbo, well-liked all around) and before they went they stopped by the drugstore and bought movies snacks. Apparently our 8yo daughter, remembering Daddy's favorite candy, convinced Mom to buy a box of Reese's Pieces.

After the movie and a couple more errands, they came home, at which time our youngest called out something akin to "No Peeeeeking" and disappeared into her room. 20 minutes later she appeared in my office with a note that said (she's somewhat developmentally delayed) "Daddy <her name> romm for You Lov <her name>". She excitedly communicated that this was a hint and I was to accompany her to her room, where I got to search her room for a present.

When I found and opened the small gift bag under her pillow containing a wrapped-with-a-bow box of candy, my heart simply melted. How did I deserve such love and adoration?