On 08/25/2016 04:37 PM, Seth P wrote:
If I understand what you're saying, the problem is that set
_creation_order() specifies an ordering across all columns from all
mixins. But shouldn't it suffice to specify the "local" ordering of the
columns within a given mixin, and then process the mixins in __mro__ order?
the way set_creation_order() works is by assigning a counter to an
object when it is actually created, not when it is encountered in a
class definition.
That's how we get around:
class Foo(object):
attr_one = some_attr("im first!")
attr_two = some_attr("im second!")
attr_three = some_attr("im third!")
When we get a Python metaclass for the above, attr_one/two/three are all
in an unordered dict(). So instead, there's a counter that was set up
when some_attr() was actually called.
That approach doesn't really work here:
class Foo(object):
@some_attr("im first!")
def return_a_thing(self):
return Thing()
@some_attr("im second!")
def return_another_thing(self):
return Thing()
@some_attr("im third!")
def return_a_third_thing(self):
return Thing()
that is, while we can still give a counter to some_attr(), the thing
that is calling those methods also has to be invoked in that order,
because we really want each Thing() to have the ordering, and they've
yet to be created.
You can of course try to make each Thing() with a hardcoded ordering:
class Foo(object):
@some_attr("im first!")
def return_a_thing(self):
return Thing(hardcode_ordering=100)
@some_attr("im second!")
def return_another_thing(self):
return Thing(hardcode_ordering=200)
@some_attr("im third!")
def return_a_third_thing(self):
return Thing(hardcode_ordering=300)
if you want to go that approach you can assign _creation_order to each
Column you're creating, but those numbers have to all be what you want
in relation to all the other columns being set up.
Overall in SQL it really shouldn't matter what order columns are set up
in. If you *really* need this then I'd suggest using inner __table__
style:
http://docs.sqlalchemy.org/en/rel_1_0/orm/extensions/declarative/table_config.html#using-a-hybrid-approach-with-table
(FWIW I worked around my particular problem by making the Columns
non-@declared_attr, eliminating ForeignKey parameters (which are
cls-dependent), and creating cls-dependent ForeignKeyConstraints in a
cls-dependent __table_args__.)
On Thu, Aug 25, 2016 at 4:24 PM -0400, "Mike Bayer"
<[email protected] <mailto:[email protected]>> wrote:
the @declarative_attr object would need util.set_creation_order()
applied and the _MapperConfig._scan_attributes() would need to take this
into account. However, it would not behave well across multiple mixins.
The mixins must be scanned in __mro__ order first. So it would be of
limited use for there to be an ordering under @declared_attr.
On 08/25/2016 02:46 PM, Seth P wrote:
> I was just bitten by this issue. Is it still the case that there is no
way to specify the order of two columns declared in a mixin using @declared_attr?
>
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