id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
22999	Impossible to generate migration for model with dynamic upload_to field	Kevin Van Wilder <kevin@…>	nobody	"In my application I have a model which uploads forms to a specific user directory for better file system organization:

media_root/<username>/reports/file

To accomplish this, I use the following model:


{{{
upload_dir = upload_to_student_dir('committee/reports/')


class CommitteeReport(TimeStampedModel):
    user = models.ForeignKey(User)
    document = models.FileField(upload_to=upload_dir)
}}}


The function defines and returns an inner function which will provide the complete path based on the instance's user:


{{{
def upload_to_student_dir(sub_path=''):
    def callable(instance, filename):
        """"""Dynamically returns the user directory to which this file should be uploaded.
        """"""
        path = ""students/{0}/{1}{2}"".format(instance.user.username, sub_path, filename)
        return path
    return callable
}}}

Creating a migration via South seemed to have caused no problems, yet the analysis being employed by django.db.migrations differs and generates the following error:


{{{
Migrations for 'committee':
  0001_initial.py:
    - Create model CommitteeReport
Traceback (most recent call last):
  File ""manage.py"", line 11, in <module>
    execute_from_command_line(sys.argv)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/core/management/__init__.py"", line 385, in execute_from_command_line
    utility.execute()
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/core/management/__init__.py"", line 377, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/core/management/base.py"", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/core/management/base.py"", line 337, in execute
    output = self.handle(*args, **options)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/core/management/commands/makemigrations.py"", line 115, in handle
    self.write_migration_files(changes)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/core/management/commands/makemigrations.py"", line 143, in write_migration_files
    migration_string = writer.as_string()
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/db/migrations/writer.py"", line 124, in as_string
    operation_string, operation_imports = OperationWriter(operation).serialize()
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/db/migrations/writer.py"", line 76, in serialize
    arg_string, arg_imports = MigrationWriter.serialize(item)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/db/migrations/writer.py"", line 229, in serialize
    item_string, item_imports = cls.serialize(item)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/db/migrations/writer.py"", line 290, in serialize
    return cls.serialize_deconstructed(path, args, kwargs)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/db/migrations/writer.py"", line 205, in serialize_deconstructed
    arg_string, arg_imports = cls.serialize(arg)
  File ""/home/kevin/.virtualenvs/stageportfolio/local/lib/python2.7/site-packages/django/db/migrations/writer.py"", line 316, in serialize
    ""Could not find function %s in %s.\nPlease note that ""
ValueError: Could not find function %s in %s.
Please note that due to Python 2 limitations, you cannot serialize unbound method functions (e.g. a method declared
and used in the same class body). Please move the function into the main module body to use migrations.
For more information, see https://docs.djangoproject.com/en/1.7/topics/migrations/#serializing-values
}}}

As you can see I have already moved the function into the main module, yet the error persists."	Bug	closed	Migrations	1.7-rc-1	Normal	invalid			Unreviewed	0	0	0	0	0	0