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
22851	Default value for BinaryField	wkschwartz@…	Andrew Godwin	"django.db.backends.schema.BaseDatabaseSchemaEditor.effective_default (https://github.com/django/django/blob/1.7b4/django/db/backends/schema.py#L157) selects """" as the default value if none is given for a BinaryField. When you try to migrate for the first time, you'll get an error.

== Temporary workaround ==

If you have a BinaryField that you want to have both null=True and editable=False, make sure to give it an explicit default of a bytes value such as b"""".


== Steps to reproduce ==


0. Use '''Python 3.4.1 and Django 1.7b4'''.
1. Make an empty project with a single empty app called ''a''.
2. Make ''a''/models.py read as follows:

{{{
    from django.db import models
    class M(models.Model):
        b = models.BinaryField(blank=True, editable=False)
}}}

3. Add ''a'' to settings.py's INSTALLED_APPS
4. ./manage.py makemigrations ''a''
5. ./manage.py migrate

You should see the following error:

{{{
  Applying bt.0001_initial...Traceback (most recent call last):
  File ""./manage.py"", line 10, in <module>
    execute_from_command_line(sys.argv)
  File ""venv3/lib/python3.4/site-packages/django/core/management/__init__.py"", line 427, in execute_from_command_line
    utility.execute()
  File ""venv3/lib/python3.4/site-packages/django/core/management/__init__.py"", line 419, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File ""venv3/lib/python3.4/site-packages/django/core/management/base.py"", line 288, in run_from_argv
    self.execute(*args, **options.__dict__)
  File ""venv3/lib/python3.4/site-packages/django/core/management/base.py"", line 337, in execute
    output = self.handle(*args, **options)
  File ""venv3/lib/python3.4/site-packages/django/core/management/commands/migrate.py"", line 146, in handle
    executor.migrate(targets, plan, fake=options.get(""fake"", False))
  File ""venv3/lib/python3.4/site-packages/django/db/migrations/executor.py"", line 62, in migrate
    self.apply_migration(migration, fake=fake)
  File ""venv3/lib/python3.4/site-packages/django/db/migrations/executor.py"", line 96, in apply_migration
    migration.apply(project_state, schema_editor)
  File ""venv3/lib/python3.4/site-packages/django/db/migrations/migration.py"", line 107, in apply
    operation.database_forwards(self.app_label, schema_editor, project_state, new_state)
  File ""venv3/lib/python3.4/site-packages/django/db/migrations/operations/models.py"", line 30, in database_forwards
    schema_editor.create_model(model)
  File ""venv3/lib/python3.4/site-packages/django/db/backends/schema.py"", line 197, in create_model
    definition, extra_params = self.column_sql(model, field)
  File ""venv3/lib/python3.4/site-packages/django/db/backends/schema.py"", line 120, in column_sql
    default_value = self.effective_default(field)
  File ""venv3/lib/python3.4/site-packages/django/db/backends/schema.py"", line 172, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File ""venv3/lib/python3.4/site-packages/django/db/models/fields/__init__.py"", line 625, in get_db_prep_save
    prepared=False)
  File ""venv3/lib/python3.4/site-packages/django/db/models/fields/__init__.py"", line 2023, in get_db_prep_value
    return connection.Database.Binary(value)
  TypeError: memoryview: str object does not have the buffer interface
}}}


== Suggested fix ==

The aforementioned effective_default method should detect BinaryFields and if they allow empty strings, give them a default value of the empty bytes string rather than Unicode string. Specifically, this is probably a problem on Python 3 more so than Python 2."	Bug	closed	Migrations	dev	Release blocker	fixed	binaryfield, default		Accepted	0	0	0	0	0	0