Thanks Michael!
"Properly" was a poor choice of words on my part. Yes, of course, == is
overloaded to make where (etc) clauses pretty, I just didn't put two and two
together.
--jack
On Wed, Jan 21, 2009 at 5:38 PM, Michael Bayer <mike...@zzzcomputing.com>wrote:
>
>
> On Jan 21, 2009, at 7:46 PM, Jack Stahl wrote:
>
> > Hello,
> >
> > I've got a few SQL interfaces where I'd like to change my query
> > based on the columns required by the client. For example, in one
> > situation, I only join against my User table if my client requires a
> > photo id:
> >
> > # cols is the list of columns the client would like selected
> > if User.c.photo_id in cols:
> > table = table.join(User.table)
> >
> > In another situation, I'd like to include the flags column in the
> > query even if the client ask for it
> >
> > if not cols:
> > cols = [cls]
> > elif not (cls.c.flags in cols):
> > # ensure flags are there so we can add "is_active"
> > cols.append(cls.c.flags)
> >
> > However, my tests for membership pass regardless of whether column
> > is actually in the list cols. That is,
> >
> > Column('flags', BitField(), table=<foo_table>) in [Column('foo',
> > String(length=84, convert_unicode=False, assert_unicode=None),
> > table=<foo_table>), Column('bar', Text(length=None,
> > convert_unicode=False, table=<foo_table>)]
> >
> > evaluates to True
> >
> > Is the == operator not properly implemented for SQLAlchemy Columns?
> > (I'm using version 0.42)
>
> it is not "properly" implemented in the sense that it does not return
> True or False, but if you''ve used SQLalchemy, you'd know that we
> redefine the "==" operator to return ClauseElement objects. That's
> why you can say somecolumn==5 and get an expression from it.
>
> So you cannot use the "in" operator to search for a Column object in a
> list. The solution however is simple. Use a set() instead, where the
> objects will be compared based on the return value of __hash__() which
> results in an object identity comparison.
>
> if User.c.photo_id in set(cols):
>
>
> >
>
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