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from __future__ import unicode_literals
from copy import deepcopy
import django
from django.core.exceptions import FieldError
from django.db import models
from django.db.models.query_utils import DeferredAttribute
class FieldInstanceTracker(object):
def __init__(self, instance, fields, field_map):
self.instance = instance
self.fields = fields
self.field_map = field_map
self.init_deferred_fields()
def get_field_value(self, field):
return getattr(self.instance, self.field_map[field])
def set_saved_fields(self, fields=None):
if not self.instance.pk:
self.saved_data = {}
elif fields is None:
self.saved_data = self.current()
else:
self.saved_data.update(**self.current(fields=fields))
# preventing mutable fields side effects
for field, field_value in self.saved_data.items():
self.saved_data[field] = deepcopy(field_value)
def current(self, fields=None):
"""Returns dict of current values for all tracked fields"""
if fields is None:
if self.instance._deferred_fields:
fields = [
field for field in self.fields
if field not in self.instance._deferred_fields
]
else:
fields = self.fields
return dict((f, self.get_field_value(f)) for f in fields)
def has_changed(self, field):
"""Returns ``True`` if field has changed from currently saved value"""
if field in self.fields:
return self.previous(field) != self.get_field_value(field)
else:
raise FieldError('field "%s" not tracked' % field)
def previous(self, field):
"""Returns currently saved value of given field"""
return self.saved_data.get(field)
def changed(self):
"""Returns dict of fields that changed since save (with old values)"""
return dict(
(field, self.previous(field))
for field in self.fields
if self.has_changed(field)
)
def init_deferred_fields(self):
self.instance._deferred_fields = set()
if hasattr(self.instance, '_deferred') and not self.instance._deferred:
return
class DeferredAttributeTracker(DeferredAttribute):
def __get__(field, instance, owner):
if instance is None:
return field
data = instance.__dict__
if data.get(field.field_name, field) is field:
instance._deferred_fields.remove(field.field_name)
value = super(DeferredAttributeTracker, field).__get__(
instance, owner)
self.saved_data[field.field_name] = deepcopy(value)
return data[field.field_name]
if django.VERSION >= (1, 8):
self.instance._deferred_fields = self.instance.get_deferred_fields()
for field in self.instance._deferred_fields:
if django.VERSION >= (1, 10):
field_obj = getattr(self.instance.__class__, field)
else:
field_obj = self.instance.__class__.__dict__.get(field)
field_tracker = DeferredAttributeTracker(
field_obj.field_name, None)
setattr(self.instance.__class__, field, field_tracker)
else:
for field in self.fields:
field_obj = self.instance.__class__.__dict__.get(field)
if isinstance(field_obj, DeferredAttribute):
self.instance._deferred_fields.add(field)
# Django 1.4
if django.VERSION >= (1, 5):
model = None
else:
model = field_obj.model_ref()
field_tracker = DeferredAttributeTracker(
field_obj.field_name, model)
setattr(self.instance.__class__, field, field_tracker)
class FieldTracker(object):
tracker_class = FieldInstanceTracker
def __init__(self, fields=None):
self.fields = fields
def get_field_map(self, cls):
"""Returns dict mapping fields names to model attribute names"""
field_map = dict((field, field) for field in self.fields)
all_fields = dict((f.name, f.attname) for f in cls._meta.fields)
field_map.update(**dict((k, v) for (k, v) in all_fields.items()
if k in field_map))
return field_map
def contribute_to_class(self, cls, name):
self.name = name
self.attname = '_%s' % name
models.signals.class_prepared.connect(self.finalize_class, sender=cls)
def finalize_class(self, sender, **kwargs):
if self.fields is None:
self.fields = (field.attname for field in sender._meta.fields)
self.fields = set(self.fields)
self.field_map = self.get_field_map(sender)
models.signals.post_init.connect(self.initialize_tracker)
self.model_class = sender
setattr(sender, self.name, self)
def initialize_tracker(self, sender, instance, **kwargs):
if not isinstance(instance, self.model_class):
return # Only init instances of given model (including children)
tracker = self.tracker_class(instance, self.fields, self.field_map)
setattr(instance, self.attname, tracker)
tracker.set_saved_fields()
self.patch_save(instance)
def patch_save(self, instance):
original_save = instance.save
def save(**kwargs):
ret = original_save(**kwargs)
update_fields = kwargs.get('update_fields')
if not update_fields and update_fields is not None: # () or []
fields = update_fields
elif update_fields is None:
fields = None
else:
fields = (
field for field in update_fields if
field in self.fields
)
getattr(instance, self.attname).set_saved_fields(
fields=fields
)
return ret
instance.save = save
def __get__(self, instance, owner):
if instance is None:
return self
else:
return getattr(instance, self.attname)
class ModelInstanceTracker(FieldInstanceTracker):
def has_changed(self, field):
"""Returns ``True`` if field has changed from currently saved value"""
if not self.instance.pk:
return True
elif field in self.saved_data:
return self.previous(field) != self.get_field_value(field)
else:
raise FieldError('field "%s" not tracked' % field)
def changed(self):
"""Returns dict of fields that changed since save (with old values)"""
if not self.instance.pk:
return {}
saved = self.saved_data.items()
current = self.current()
return dict((k, v) for k, v in saved if v != current[k])
class ModelTracker(FieldTracker):
tracker_class = ModelInstanceTracker
def get_field_map(self, cls):
return dict((field, field) for field in self.fields)
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