On Apr 3, 11:45 am, Adam Dziendziel <[EMAIL PROTECTED]> wrote:
>
> Then, I set a primary key indirectly:
>
> translation = CategoryTranslation()
> translation.category = session.query(Category).filter(....).one()
> translation.language = session.query(Language).filter(....).one()
>
> 1. How to check whether the primary key is set? I cannot simply check
> if every column of class_mapper(CategoryTranslation).primary_key is
> set, because these field are empty until I save save the object.
i would rephrase this question as, "how to check if a required foreign
key constraint will be fulfilled based on the interactions of an
instance with related instances". an entirely generic way might be:
from sqlalchemy.orm import sync
def manytoones_are_set(instance):
for prop in object_mapper(instance).iterate_properties:
if getattr(prop, 'direction', None) == sync.MANYTOONE:
if not getattr(instance, prop.key):
return False
else:
return True
> 2. How to retrieve that key? I would like to check if the record
> already exists.
This is a great question for me because coming up with the function
for this revealed a terrific refactoring I think I'm going to try.
This function will work for single-valued primary and foreign keys.
For a multiple valued pk/fk, there is a more complicated function that
can work here, but my refactoring will involve making the "local_side"
and "remote_side" collections on PropertyLoader ordered, so that
questions like these can be answered more easily:
def manytoone_columns(instance):
mapper = object_mapper(instance)
for prop in mapper.iterate_properties:
if getattr(prop, 'direction', None) == sync.MANYTOONE:
local, remote = list(prop.local_side)[0],
list(prop.remote_side)[0]
value = getattr(instance, prop.key)
remote_value = getattr(value, remote.key)
yield (local, remote_value)
def apparent_primary_key(instance):
mapper = object_mapper(instance)
values = dict(list(manytoone_columns(instance)))
for col in mapper.primary_key:
if col in values:
yield values[col]
else:
yield getattr(instance, col.key)
print list(apparent_primary_key(some_instance))
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