Howdy Folks,
I have been testing model inheritance using models that have UUIDField
primary keys. It appears that when you save a new instance of a child
model, the framework is not calling get_db_prep_value() to convert the
UUIDField to a proper format before querying the parent entry.
Let's say we have two very simple models:
class Person(models.Model):
id = UUIDField(primary_key=True)
name = models.CharField(max_length=32)
class Child(Person):
grade = models.SmallIntegerField()
If you do this...
c = Child(name="Mary", grade=5)
c.save()
...the framework will first create the myapp_person entry. Then it
does a query like this:
SELECT (1) AS "a" FROM "myapp_child" WHERE
"myapp_child"."person_ptr_id" = %s
I put some print statement in all of the methods in UUIDField, and
none of them are being called before that statement is executed,
including: get_db_prep_lookup, get_db_prep_value, get_db_prep_save,
pre_save
The result is an error from the database:
<class 'psycopg2.ProgrammingError'>: can't adapt
Interesting note... the psycopg driver doesn't generate an error.
Even though it is an older driver, apparently is is less picky about
the parameters. Psycopg will accept a uuid object in the statement
that fails and apperently psycopg2 wants it cast to a string.
If anyone has an idea I would love to hear it.
By the way, I'm using a modified version of the UUIDField from the
django-extensions project. This is one that uses a native uuid field
for the database when the backend supports it (postgresql) and a
charfield when the backend doesn't support it (others). I did some
tests and performance with postgresql is better with the native type
(not suprising).
--gordon
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