TypeError creating new instance of automapped model from table named items

Question

I have a database with a table named "items":

import sqlite3

stmt = """CREATE TABLE items (id INTEGER PRIMARY KEY, name TEXT)"""
conn = sqlite3.connect('test20210101.db')
conn.execute(stmt)

I use SQLAlchemy's automap feature to map the table to a model class:

import sqlalchemy as sa
from sqlalchemy.ext.automap import automap_base

engine = sa.create_engine('sqlite:///test20210101.db')
Base = automap_base()
Base.prepare(engine, reflect=True)
Item = Base.classes.items

However if I try to create a new item, I get a TypeError :

>>> new_item = Item(name='foo')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: items() got an unexpected keyword argument 'name'

Likewise attempts to query the database using the automapped model fail:

>>> items = session.query(Item).all()
Traceback (most recent call last):
   <lots of traceback>
sqlalchemy.exc.ArgumentError: Column expression or FROM clause expected, got ('items', <class 'sqlalchemy.ext.automap.items'>).

Similar code works for other tables, what's going on here?

Answer 1

As the raising of TypeError suggests, the problem is that Item is not an automapped model as we would expect. In fact it's a method object:

>>> type(Item)
<class 'method'>
>>> Item
<bound method Properties.items of <sqlalchemy.util._collections.Properties object at 0x7fb088f48fa0>>

The problem is that Base.classes exposes a dictionary-like API, and Base.classes.items is the API's items method rather than the automapped object*.

There are at least two ways to work around this name collision:

• access the automapped object using __getitem__

   >>> Item = Base.classes['items'] >>> Item <class 'sqlalchemy.ext.automap.items'>

• define a custom function to map table names to class names when preparing the Base

  >>> def map_names(base, tablename, table): ... return 'my_items' if tablename == 'items' else tablename... >>> Base = automap_base() >>> Base.prepare(engine, reflect=True, classname_for_table=map_names) >>> Item = Base.classes.my_items >>> Item <class 'sqlalchemy.ext.automap.my_items'>

---

* So the same problem occurs for other dict-related names, for example keys , values etc.

Answer 2

You are importing the file not the class Item

change:

import Item

to

from Item import Item