[sqlalchemy] Re: checking if a column is in a list
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):
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
sqlalchemy group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~--~~~~--~~--~--~---
[sqlalchemy] Re: checking if a column is in a list
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.comwrote:
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):
--~--~-~--~~~---~--~~
You received this message because you are subscribed to the Google Groups
sqlalchemy group.
To post to this group, send email to sqlalchemy@googlegroups.com
To unsubscribe from this group, send email to
sqlalchemy+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sqlalchemy?hl=en
-~--~~~~--~~--~--~---
