its because your post mapper is using joined table inheritance, i.e. joining text_items to posts. so the primary key of "text_items JOIN posts on text_items.id==posts.id" is a composite of "text_items.id, posts.id". So.....it considers the primary key of Post id #1 to be this:

        m.get(1,1)

or in 0.2, like:

        m.get((1,1))

there is the notion that the primary key of such a join should only use the single column from "text_items", since the primary key of "posts" is also the foreign key thats being related to text_items; its redundant and thats why you intuitively used only one primary key value in your get() (and also why get_by works).

but it seems like Join object is going to have to analyze the join condition to see if there is literally a "table1.primary_key==table2.foreign_and_primary_key" condition since there are other join conditions with two tables like this where this rule wouldnt apply. that will require some elaborate logic.....so i think you have to stick with the "dual id" thing for the near term.

On May 17, 2006, at 5:41 PM, Marty McFly wrote:

Hi everybody, here's a small script using mapper inheritance that fails on my machine (SQLAlchemy 0.1.7, Python 2.4.2). The following line at the end of the script below causes an error:

firstTry = Post.mapper.get(1)

Whereas the next line works fine
secondTry = Post.mapper.get_by(id=1)

Is it a bug or a mistake on my part? Here's the sample script in case anybody wants to test the whole thing:

----------------------------------------------------
from sqlalchemy import *

engine = create_engine('mysql',
        {
            'db':'sqlalchemy',
            'user':'myself',
            'passwd':'mypassword',
            'host':'127.0.0.1'

        },
        )

text_items = Table('text_items', engine,
    Column('id', Integer, primary_key=True),
    Column('text', String)
)

posts = Table('posts', engine,
Column('id', Integer, ForeignKey("text_items.id"), primary_key=True),
    Column('headline', String)
)

text_items.create()
posts.create()

class TextItem(object):
    pass

class Post(TextItem):
    pass


TextItem.mapper = mapper(TextItem, text_items)
Post.mapper = mapper(Post, posts,
                     inherits=TextItem.mapper,
                     )

post = Post()
post.text = "it pretty much always means no"
post.headline = "maybe"
objectstore.commit()

firstTry = Post.mapper.get(1)
secondTry = Post.mapper.get_by(id=1)

-------------------------------------------
Here's the traceback from the "first try":

Traceback (most recent call last):
  File "<stdin>", line 1, in ?
File "build\bdist.win32\egg\sqlalchemy\mapping\mapper.py", line 251, in get File "build\bdist.win32\egg\sqlalchemy\mapping\query.py", line 43, in get File "build\bdist.win32\egg\sqlalchemy\mapping\query.py", line 201, in _get
IndexError: tuple index out of range

The "second try" works fine.

Thanks and cheers, Martin

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