[sqlalchemy] Re: ORM ramblings 2 - and announcing some o2r wrapper

[svilen]

if you read closely, you can see that the embedded query for
selecting the employee is wrong; it has no FROM clause:

SELECT "Employee".id AS id, "Employee".name AS name,
"Employee".atype AS atype, "Employee".manager_id AS manager_id
\nWHERE "Employee".atype = ?

SQLite is a little dumb in that it doesnt give a reasonable error
message for this condition (other DB's do).

when you see a SELECT that has no FROM, it usually means SA is
trying to "correlate" the select as a subquery to the enclosing
query.  this will occur anytime a select involving the "employee"


so the "fix" is just to insure that the subquery doesnt get
"correlated":

ajoin = {
    'Employee': employee_table.select( employee_table.c.atype
=='Employee', correlate=False),
    'Manager': join( employee_table,
manager_table,manager_table.c.id ==employee_table.c.id),
}

and all is well again.

table occurs within another select involving the "employee" table. in this case its clearly wrong.

okay, would the join() also need .select(correlate=False) on it, or SA will not mistake it?

Next variant, if tables are concrete, it does same mistake - so i have to specify employee_table.select( correlate=False) instead of plain employee_table in the polymorphic_union. Anything else? And, as i understand this applies only to things that go in a polymorphic_union; otherwise the correlate=False is not needed.

the polymorphic union thing is one of the most ambitious queries
SQLAlchemy's ORM produces.  which is why I still have not made it

Speaking of polyunion, i have made another version of your helper function. Your variant works ok if all tables under the poly-base are inherited in same way, i.e. either all are concrete_table, or all are table_inheritance. My version (~5-6 lines changed) does not require this (see attached file), and works ok for any type of mixed inheritance.

ciao
svil

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btw, this correlate=False can be added automaticaly in the polyunion(). i've added it there and it seems to work... What do u think?

polymunion.py
Description: application/python