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import sqlalchemy as sa
class ProxyDict:
def __init__(self, parent, collection_name, mapping_attr):
self.parent = parent
self.collection_name = collection_name
self.child_class = mapping_attr.class_
self.key_name = mapping_attr.key
self.cache = {}
@property
def collection(self):
return getattr(self.parent, self.collection_name)
def keys(self):
descriptor = getattr(self.child_class, self.key_name)
return [x[0] for x in self.collection.values(descriptor)]
def __contains__(self, key):
if key in self.cache:
return self.cache[key] is not None
return self.fetch(key) is not None
def has_key(self, key):
return self.__contains__(key)
def fetch(self, key):
session = sa.orm.object_session(self.parent)
if session and sa.orm.util.has_identity(self.parent):
obj = self.collection.filter_by(**{self.key_name: key}).first()
self.cache[key] = obj
return obj
def create_new_instance(self, key):
value = self.child_class(**{self.key_name: key})
self.collection.append(value)
self.cache[key] = value
return value
def __getitem__(self, key):
if key in self.cache:
if self.cache[key] is not None:
return self.cache[key]
else:
value = self.fetch(key)
if value:
return value
return self.create_new_instance(key)
def __setitem__(self, key, value):
try:
existing = self[key]
self.collection.remove(existing)
except KeyError:
pass
self.collection.append(value)
self.cache[key] = value
def proxy_dict(parent, collection_name, mapping_attr):
try:
parent._proxy_dicts
except AttributeError:
parent._proxy_dicts = {}
try:
return parent._proxy_dicts[collection_name]
except KeyError:
parent._proxy_dicts[collection_name] = ProxyDict(
parent,
collection_name,
mapping_attr
)
return parent._proxy_dicts[collection_name]
def expire_proxy_dicts(target, context):
if hasattr(target, '_proxy_dicts'):
target._proxy_dicts = {}
sa.event.listen(sa.orm.Mapper, 'expire', expire_proxy_dicts)
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