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"""
Convenience routines for creating non-trivial Field subclasses, as well as
backwards compatibility utilities.
Add SubfieldBase as the __metaclass__ for your Field subclass, implement
to_python() and the other necessary methods and everything will work seamlessly.
"""
from inspect import getargspec
from warnings import warn
def call_with_connection(func):
arg_names, varargs, varkwargs, defaults = getargspec(func)
updated = ('connection' in arg_names or varkwargs)
if not updated:
warn("A Field class whose %s method hasn't been updated to take a "
"`connection` argument." % func.__name__,
PendingDeprecationWarning, stacklevel=2)
def inner(*args, **kwargs):
if 'connection' not in kwargs:
from django.db import connection
kwargs['connection'] = connection
warn("%s has been called without providing a connection argument. " %
func.__name__, PendingDeprecationWarning,
stacklevel=1)
if updated:
return func(*args, **kwargs)
if 'connection' in kwargs:
del kwargs['connection']
return func(*args, **kwargs)
return inner
def call_with_connection_and_prepared(func):
arg_names, varargs, varkwargs, defaults = getargspec(func)
updated = (
('connection' in arg_names or varkwargs) and
('prepared' in arg_names or varkwargs)
)
if not updated:
warn("A Field class whose %s method hasn't been updated to take "
"`connection` and `prepared` arguments." % func.__name__,
PendingDeprecationWarning, stacklevel=2)
def inner(*args, **kwargs):
if 'connection' not in kwargs:
from django.db import connection
kwargs['connection'] = connection
warn("%s has been called without providing a connection argument. " %
func.__name__, PendingDeprecationWarning,
stacklevel=1)
if updated:
return func(*args, **kwargs)
if 'connection' in kwargs:
del kwargs['connection']
if 'prepared' in kwargs:
del kwargs['prepared']
return func(*args, **kwargs)
return inner
class LegacyConnection(type):
"""
A metaclass to normalize arguments give to the get_db_prep_* and db_type
methods on fields.
"""
def __new__(cls, names, bases, attrs):
new_cls = super(LegacyConnection, cls).__new__(cls, names, bases, attrs)
for attr in ('db_type', 'get_db_prep_save'):
setattr(new_cls, attr, call_with_connection(getattr(new_cls, attr)))
for attr in ('get_db_prep_lookup', 'get_db_prep_value'):
setattr(new_cls, attr, call_with_connection_and_prepared(getattr(new_cls, attr)))
return new_cls
class SubfieldBase(LegacyConnection):
"""
A metaclass for custom Field subclasses. This ensures the model's attribute
has the descriptor protocol attached to it.
"""
def __new__(cls, base, name, attrs):
new_class = super(SubfieldBase, cls).__new__(cls, base, name, attrs)
new_class.contribute_to_class = make_contrib(
attrs.get('contribute_to_class'))
return new_class
class Creator(object):
"""
A placeholder class that provides a way to set the attribute on the model.
"""
def __init__(self, field):
self.field = field
def __get__(self, obj, type=None):
if obj is None:
raise AttributeError('Can only be accessed via an instance.')
return obj.__dict__[self.field.name]
def __set__(self, obj, value):
obj.__dict__[self.field.name] = self.field.to_python(value)
def make_contrib(func=None):
"""
Returns a suitable contribute_to_class() method for the Field subclass.
If 'func' is passed in, it is the existing contribute_to_class() method on
the subclass and it is called before anything else. It is assumed in this
case that the existing contribute_to_class() calls all the necessary
superclass methods.
"""
def contribute_to_class(self, cls, name):
if func:
func(self, cls, name)
else:
super(self.__class__, self).contribute_to_class(cls, name)
setattr(cls, self.name, Creator(self))
return contribute_to_class
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