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