On 12/16/2016 07:42 AM, Balázs Gibizer wrote:
Hi,
What is the expected behavior of accessing a nullable and
not set versioned object field?
See the following example code:
from oslo_versionedobjects import base
from oslo_versionedobjects import fields
@base.VersionedObjectRegistry.register
class MyObject(base.VersionedObject):
VERSION = '1.0'
fields = {
'nullable_string': fields.StringField(nullable=True),
}
my_obj = MyObject()
my_obj.nullable_string
#EOF
My naïve expectation would be that the value of my_obj.nullable_string
is None but the actual behavior is an exception:
Traceback (most recent call last):
File "ovo_nullable_test.py", line 15, in <module>
my_obj.nullable_string
File
".tox/functional/local/lib/python2.7/site-packages/oslo_versionedobjects/base.py",
line 67, in getter
self.obj_load_attr(name)
File
".tox/functional/local/lib/python2.7/site-packages/oslo_versionedobjects/base.py",
line 603, in obj_load_attr
_("Cannot load '%s' in the base class") % attrname)
NotImplementedError: Cannot load 'nullable_string' in the base class
Is this the correct behavior?
Yes, that's the expected behaviour.
Then what is the expected behavior if the field is also defaulted to None?
fields = {
'nullable_string': fields.StringField(nullable=True, default=None),
}
The actual behavior is still the same exception above. Is it the correct
behavior?
Yes. So, what the default=None does is describe the behaviour of the
field when obj_set_defaults() is called. It does *not* describe what is
returned if the field *value* is accessed before being populated.
What you're looking for is the obj_attr_is_set() method:
if MyObject.obj_attr_is_set('nullable_string'):
print my_obj.nullable_string
In addition to the obj_attr_is_set() method, use the obj_set_defaults()
method to manually set all fields that have a default=XXX value to XXX
if those fields have not yet been manually set:
class MyObject(ovo.VersionedObjectBase):
def create(self):
self.obj_set_defaults()
# Now you can access your nullable_string field.
The reason this was done was to allow us to differentiate between fields
that had not had their value set and fields that HAD had their attribute
set, but to None.
Best,
-jay
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