On 09/22/2016 01:29 PM, Chris Withers wrote:
On 22/09/2016 14:55, Mike Bayer wrote:
On 09/22/2016 07:30 AM, Chris Withers wrote:
How do you control the order in which columns are added to a
multi-column primary key when using the declarative primary_key=True
syntax?
How about when one of those columns comes from a mixin?
without mixins, the columns are processed in the order that they were
created - they all have a global "created index" number that is
consulted outside of the order in which the objects appear on a
declarative class.
Right, so you'd just re-order the columns...
With mixins, that all gets screwed up. In that case you'd use a
PrimaryKeyConstraint() object on the final mapped class and that will
express the ordering of the columns.
...which I guess I'd want to introspect and then form that final
PrimaryKeyConstraint. How would I do that in this mixin:
https://github.com/Mortar/mortar_mixins/blob/master/mortar_mixins/temporal.py
...while also removing the primary key generated by the primary_key=True
on the various columns?
you know I bet you could use an event hook to just catch that when the
Table is first set up and just re-set the PrimaryKeyConstraint. I
thought this could be done with a simple after_parent_attach but that
seems to occur in an inopportune place. so we'll get the table when
it's done totally:
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event, PrimaryKeyConstraint
Base = declarative_base()
@event.listens_for(Base, "instrument_class", propagate=True)
def instrument_class(mapper, class_):
mapper.local_table.append_constraint(
PrimaryKeyConstraint(
*sorted(list(mapper.local_table.primary_key),
key=lambda column: column.key))
)
class Z(object):
z = Column(Integer, primary_key=True)
class A(Z, Base):
__tablename__ = 'a'
x = Column(Integer, primary_key=True)
y = Column(Integer, primary_key=True)
from sqlalchemy.schema import CreateTable
print CreateTable(A.__table__)
cheers,
Chris
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