├── model_update.py
├── nullable_foreignkey.py
└── staff_debug_wsgi_handler.py


/model_update.py:
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 1 | import operator
 2 | 
 3 | from django.db.models.expressions import F, ExpressionNode
 4 | 
 5 | EXPRESSION_NODE_CALLBACKS = {
 6 |     ExpressionNode.ADD: operator.add,
 7 |     ExpressionNode.SUB: operator.sub,
 8 |     ExpressionNode.MUL: operator.mul,
 9 |     ExpressionNode.DIV: operator.div,
10 |     ExpressionNode.MOD: operator.mod,
11 |     ExpressionNode.AND: operator.and_,
12 |     ExpressionNode.OR: operator.or_,
13 |     }
14 | 
15 | class CannotResolve(Exception):
16 |     pass
17 | 
18 | def _resolve(instance, node):
19 |     if isinstance(node, F):
20 |         return getattr(instance, node.name)
21 |     elif isinstance(node, ExpressionNode):
22 |         return _resolve(instance, node)
23 |     return node
24 | 
25 | def resolve_expression_node(instance, node):
26 |     op = EXPRESSION_NODE_CALLBACKS.get(node.connector, None)
27 |     if not op:
28 |         raise CannotResolve
29 |     runner = _resolve(instance, node.children[0])
30 |     for n in node.children[1:]:
31 |         runner = op(runner, _resolve(instance, n))
32 |     return runner
33 | 
34 | def update(instance, **kwargs):
35 |     "Atomically update instance, setting field/value pairs from kwargs"
36 |     # fields that use auto_now=True should be updated corrected, too!
37 |     for field in instance._meta.fields:
38 |         if hasattr(field, 'auto_now') and field.auto_now and field.name not in kwargs:
39 |             kwargs[field.name] = field.pre_save(instance, False)
40 | 
41 |     rows_affected = instance.__class__._default_manager.filter(pk=instance.pk).update(**kwargs)
42 | 
43 |     # apply the updated args to the instance to mimic the change
44 |     # note that these might slightly differ from the true database values
45 |     # as the DB could have been updated by another thread. callers should
46 |     # retrieve a new copy of the object if up-to-date values are required
47 |     for k,v in kwargs.iteritems():
48 |         if isinstance(v, ExpressionNode):
49 |             v = resolve_expression_node(instance, v)
50 |         setattr(instance, k, v)
51 | 
52 |     # If you use an ORM cache, make sure to invalidate the instance!
53 |     #cache.set(djangocache.get_cache_key(instance=instance), None, 5)
54 |     return rows_affected
55 | 


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/nullable_foreignkey.py:
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 1 | from django.db import connection, models
 2 | 
 3 | class NullableForeignKey(models.ForeignKey):
 4 |     """
 5 |     Prevent the default CASCADE DELETE behavior of normal ForeignKey.
 6 |     When an instance pointed to by a NullableForeignKey is deleted,
 7 |     the NullableForeignKey field is NULLed rather than the row being deleted.
 8 |     """ 
 9 |     def __init__(self, *args, **kwargs):
10 |         kwargs['null'] = kwargs['blank'] = True
11 |         super(NullableForeignKey, self).__init__(*args, **kwargs)
12 | 
13 |     # Monkeypatch the related class's "collect_sub_objects"
14 |     # to not delete this object
15 |     def contribute_to_related_class(self, cls, related):
16 |         super(NullableForeignKey, self).contribute_to_related_class(cls, related)
17 |         _original_csb_attr_name = '_original_collect_sub_objects'
18 |         # define a new "collect_sub_objects" method 
19 |         this_field = self
20 |         def _new_collect_sub_objects(self, *args, **kwargs):
21 |             qn = connection.ops.quote_name
22 |             # find all fields related to the model who's instance is
23 |             # being deleted
24 |             for related in self._meta.get_all_related_objects():
25 |                 if isinstance(related.field, this_field.__class__):
26 |                     table = qn(related.model._meta.db_table)
27 |                     column = qn(related.field.column)
28 |                     sql = "UPDATE %s SET %s = NULL WHERE %s = %%s;" % (table, column, column)
29 |                     connection.cursor().execute(sql, [self.pk])
30 | 
31 |             # Now proceed with collecting sub objects that are still tied via FK
32 |             getattr(self, _original_csb_attr_name)(*args, **kwargs)
33 | 
34 |         # monkey patch the related classes _collect_sub_objects method.
35 |         # store the original method in an attr named `_original_csb_attr_name`
36 |         if not hasattr(cls, _original_csb_attr_name):
37 |             setattr(cls, _original_csb_attr_name, cls._collect_sub_objects)
38 |             setattr(cls, '_collect_sub_objects', _new_collect_sub_objects)
39 | 


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/staff_debug_wsgi_handler.py:
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 1 | from django.core.handlers import wsgi
 2 | 
 3 | class StaffDebugWSGIHandler(wsgi.WSGIHandler):
 4 |     "WSGI Handler that shows the debug error page if the logged in user is staff"
 5 | 
 6 |     def handle_uncaught_exception(self, request, resolver, exc_info):
 7 |         "Return a debug page response if the logged in user is staff"
 8 |         from django.conf import settings
 9 | 
10 |         if not settings.DEBUG and hasattr(request, 'user') and request.user.is_staff:
11 |             from django.views import debug
12 |             return debug.technical_500_response(request, *exc_info)
13 | 
14 |         # not logged in or not a staff user, display normal public 500
15 |         return super(StaffDebugWSGIHandler, self).handle_uncaught_exception(
16 |             request, resolver, exc_info
17 |             )
18 | 


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