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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