custom model fields with to_python()/from_db_value() for different django version...

[Jens Diemer]

("Moved" from django-developers list)

Am 17.06.2015 um 16:48 schrieb charettes:> Hi Jens,
>
> I'm not sure I understand what you are trying to achieve but I assume you want
> to write a third-party field that supports both Django 1.7 and 1.8 without
> raising deprecating warnings?
>
> I suggest you use the following pattern which also accounts for py2/3:
>
> import django
> from django.db import models
> from django.utils.six import with_metaclass
>
> MyFieldBase = type if django.VERSION >= (1, 8) else models.SubfieldBase
>
> class MyField(with_metaclass(MyFieldBase, models.Field)):
> def from_db_value(self, value, expression, connection, context):
> pass
>
> def to_python(self, value):
> pass
>
> This is stepping into the django-user@ territory so I suggest we move the
> discussion over there if the provided example doesn't match your needs but you
> are really just trying to write a portable third-party field.


Yes, that's my problem.

Maybe i should better check with """hasattr(models, "SubfieldBase")""" instead
of testing the version number?!?

Is this a good fallback to use 'type' ?!?

What's about this:

"""
import django
from django.db import models
from django.utils.six import with_metaclass

if hasattr(models, "SubfieldBase"):
_class_args = with_metaclass(models.SubfieldBase, models.Field)
else:
_class_args = (models.Field,)

class MyField(*_class_args):
def from_db_value(self, value, expression, connection, context):
pass

def to_python(self, value):
pass
"""


Not tested.


















> Le mercredi 17 juin 2015 06:25:09 UTC-4, Jens Diemer a écrit :
>
> Am 16.06.2015 um 18:43 schrieb Tim Graham:
> > The doc about how to ignore warnings in tests is here:
> >
>
https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#deprecating-a-feature
>
<https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/submitting-patches/#deprecating-a-feature>
>
> >
> > Alternatively, you can temporarily remove these lines in runtests.py:
> >
> > warnings.simplefilter("error", RemovedInDjango20Warning)
> > warnings.simplefilter("error", RemovedInDjango21Warning)
>
> Thanks!
>
> But then, there can't exists tests that will raise a warning while importing
> ?!?
>
>
>
>
> So i try to make it clear:
>
> With v1.7 the "__metaclass__ = models.SubfieldBase" is needed. So i
remove the
> tests without it.
>
> And i found a existing Bug https://code.djangoproject.com/ticket/9619
> <https://code.djangoproject.com/ticket/9619> for:
>
> to_python not called when fetching data with .values(...)
>
>
> I update the tests and create a ticket and pull request here:
> * https://code.djangoproject.com/ticket/24993
> <https://code.djangoproject.com/ticket/24993>
> * https://github.com/django/django/pull/4874
> <https://github.com/django/django/pull/4874>
>
> I can also made pull request for v1.8.x and master...
>
>
>
>
>
> I also found the Solution for: "to_python() didn't call with Python 3":
> The "__metaclass__" syntax changed in Python 3.
>
> The Problem: I didn't read the doc carefully here:
>
>
https://docs.djangoproject.com/en/1.7/howto/custom-model-fields/#the-subfieldbase-metaclass
>
<https://docs.djangoproject.com/en/1.7/howto/custom-model-fields/#the-subfieldbase-metaclass>
>
>
> There are three code examples:
> * for Python 2 only
> * for Python 3 only
> * for Python 2+3 using six.with_metaclass()
>
> What's about to remove the first two examples and leave only the
> six.with_metaclass() example?!?
>
> I made also a ticket/pull request for this:
> * https://code.djangoproject.com/ticket/24992
> <https://code.djangoproject.com/ticket/24992>
> * https://github.com/django/django/pull/4873
> <https://github.com/django/django/pull/4873>
>
>
>
>
>
>
>
>
>
>
>
> >
> > On Tuesday, June 16, 2015 at 12:30:05 PM UTC-4, Jens Diemer wrote:
> >
> >
> > I try to create a custom model field, that should "Converting values
> to Python
> > objects" as described in the documentation here:
> >
> >
>
<https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#converting-values-to-python-objects
>
<https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#converting-values-to-python-objects>
>
> >
>
<https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#converting-values-to-python-objects
>
<https://docs.djangoproject.com/en/dev/howto/custom-model-fields/#converting-values-to-python-objects>>>
>
> >
> >
> > It doesn't work with Python 2.7 and 3.4 with Django 1.7.x and 1.8.x...
> >
> >
> > I search around and found no unittest case for this
> "howto/custom-model-fields"
> >
> > So i created a simple test case to investigate why my code not worked.
> >
> >
> > I made a unittest against "stable/1.7.x", "stable/1.8.x" and "master"
> here:
> >
> > https://github.com/jedie/django/branches/yours
> <https://github.com/jedie/django/branches/yours>
> > <https://github.com/jedie/django/branches/yours
> <https://github.com/jedie/django/branches/yours>>
> >
> > compare links:
> >
> > stable/1.7.x
> >
>
<https://github.com/jedie/django/compare/stable/1.7.x...test_custom_model_fields_1.7.x
>
<https://github.com/jedie/django/compare/stable/1.7.x...test_custom_model_fields_1.7.x>
>
> >
>
<https://github.com/jedie/django/compare/stable/1.7.x...test_custom_model_fields_1.7.x
>
<https://github.com/jedie/django/compare/stable/1.7.x...test_custom_model_fields_1.7.x>>>
>
> >
> >
> > stable/1.8.x
> >
>
<https://github.com/jedie/django/compare/stable/1.8.x...test_custom_model_fields_1.8.x
>
<https://github.com/jedie/django/compare/stable/1.8.x...test_custom_model_fields_1.8.x>
>
> >
>
<https://github.com/jedie/django/compare/stable/1.8.x...test_custom_model_fields_1.8.x
>
<https://github.com/jedie/django/compare/stable/1.8.x...test_custom_model_fields_1.8.x>>>
>
> >
> >
> > master
> >
>
<https://github.com/jedie/django/compare/master...test_custom_model_fields_master
>
<https://github.com/jedie/django/compare/master...test_custom_model_fields_master>
>
> >
>
<https://github.com/jedie/django/compare/master...test_custom_model_fields_master
>
<https://github.com/jedie/django/compare/master...test_custom_model_fields_master>>>
>
> >
> >
> >
> > I run these test and here the result:
> >
> >
> > *** 1.7.x with Py2:
> > test_custom_model_field (custom_model_fields.tests.TestModel1Tests)
> ... FAIL
> > test_values (custom_model_fields.tests.TestModel1Tests) ... FAIL
> > test_custom_model_field (custom_model_fields.tests.TestModel2Tests)
> ... ok
> > test_values (custom_model_fields.tests.TestModel2Tests) ... FAIL
> >
> >
> > *** 1.7.x with Py3:
> > test_custom_model_field (custom_model_fields.tests.TestModel1Tests)
> ... FAIL
> > test_values (custom_model_fields.tests.TestModel1Tests) ... FAIL
> > test_custom_model_field (custom_model_fields.tests.TestModel2Tests)
> ... FAIL
> > test_values (custom_model_fields.tests.TestModel2Tests) ... FAIL
> >
> >
> >
> > *** 1.8.x with Py2:
> > test_custom_model_field (custom_model_fields.tests.TestModel1Tests)
> ... ok
> > test_values (custom_model_fields.tests.TestModel1Tests) ... ok
> >
> >
> > *** 1.8.x with Py3
> > test_custom_model_field (custom_model_fields.tests.TestModel1Tests)
> ... ok
> > test_values (custom_model_fields.tests.TestModel1Tests) ... ok
> >
> >
> >
> > *** master with Py2 - doesn't run:
> > Traceback (most recent call last):
> > File "/home/jens/PyLucid_env/src/django/tests/runtests.py", line
> 12, in
> > <module>
> > from django.apps import apps
> > File "/home/jens/PyLucid_env/src/django/django/apps/__init__.py",
> line
> > 1, in
> > <module>
> > from .config import AppConfig # NOQA
> > File "/home/jens/PyLucid_env/src/django/django/apps/config.py",
> line 6, in
> > <module>
> > from django.utils.module_loading import module_has_submodule
> > File
> "/home/jens/PyLucid_env/src/django/django/utils/module_loading.py",
> > line
> > 4, in <module>
> > from importlib import import_module
> > File
> "/home/jens/PyLucid_env/src/django/django/utils/importlib.py", line 6,
> > in <module>
> > ImportError: cannot import name RemovedInDjango19Warning
> >
> >
> >
> > *** master with Py3:
> > test_custom_model_field (custom_model_fields.tests.TestModel1Tests)
> ... ok
> > test_values (custom_model_fields.tests.TestModel1Tests) ... ok
> > test_custom_model_field (custom_model_fields.tests.TestModel2Tests)
> ... ok
> > test_values (custom_model_fields.tests.TestModel2Tests) ... ok
> >
> >
> >
> >
> > So the biggest problem is django 1.7.x...
> > But it should work in the same way:
> >
>
<https://docs.djangoproject.com/en/1.7/howto/custom-model-fields/#converting-database-values-to-python-objects
>
<https://docs.djangoproject.com/en/1.7/howto/custom-model-fields/#converting-database-values-to-python-objects>
>
> >
>
<https://docs.djangoproject.com/en/1.7/howto/custom-model-fields/#converting-database-values-to-python-objects
>
<https://docs.djangoproject.com/en/1.7/howto/custom-model-fields/#converting-database-values-to-python-objects>>>
>
> >
> >
> >
> > With 1.8.x i must remove the test with existing:
> > __metaclass__ = models.SubfieldBase
> >
> >
> > Otherwise the test will not run:
> >
> > Testing against Django installed in
> '/home/jens/PyLucid_env/src/django/django'
> > Importing application custom_model_fields
> > Traceback (most recent call last):
> > File "/home/jens/PyLucid_env/src/django/tests/runtests.py", line
> 448, in
> > <module>
> > options.debug_sql)
> > File "/home/jens/PyLucid_env/src/django/tests/runtests.py", line
> 235, in
> > django_tests
> > state = setup(verbosity, test_labels)
> > File "/home/jens/PyLucid_env/src/django/tests/runtests.py", line
> 214, in
> > setup
> > apps.set_installed_apps(settings.INSTALLED_APPS)
> > File "/home/jens/PyLucid_env/src/django/django/apps/registry.py",
> line 324,
> > in set_installed_apps
> > self.populate(installed)
> > File "/home/jens/PyLucid_env/src/django/django/apps/registry.py",
> line 108,
> > in populate
> > app_config.import_models(all_models)
> > File
"/home/jens/PyLucid_env/src/django/django/apps/config.py", line
> > 198, in
> > import_models
> > self.models_module = import_module(models_module_name)
> > File "/usr/lib/python2.7/importlib/__init__.py", line 37, in
> import_module
> > __import__(name)
> > File
> >
"/home/jens/PyLucid_env/src/django/tests/custom_model_fields/models.py",
> > line 41, in <module>
> > class CommaSeparatedModelField2(CommaSeparatedModelField1):
> > File
> >
> "/home/jens/PyLucid_env/src/django/django/db/models/fields/subclassing.py",
> > line
> > 22, in __new__
> > RemovedInDjango20Warning)
> > django.utils.deprecation.RemovedInDjango20Warning: SubfieldBase
has been
> > deprecated. Use Field.from_db_value instead.
> >
> >
> >
> > Maybe i miss something to handle warnings with tests, but didn't find
> something
> > about warnings here:
> >
> >
>
https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/
>
<https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/>
>
> >
>
<https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/
>
<https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/>>
>
> >
> >
> >
> >
> > --
> >
> >
> > Mfg.
> >
> > Jens Diemer
> >
> >
> > ----
> > http://www.jensdiemer.de
> >
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>
> --
>
>
> Mfg.
>
> Jens Diemer
>
>
> ----
> http://www.jensdiemer.de
>


--


Mfg.

Jens Diemer


----
http://www.jensdiemer.de

[Simon Charette]

Hi Jens,

I haven't tested your alternative but it looks like it would work.

I prefer the explicit check against django.VERSION since it makes it easy to search for dead code branch when dropping support a version of Django.

Simon

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