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from collections import Iterable
import six
import sqlalchemy as sa
from sqlalchemy.ext.hybrid import hybrid_property
from sqlalchemy.orm import attributes, class_mapper, ColumnProperty
from sqlalchemy.orm.interfaces import MapperProperty, PropComparator
from sqlalchemy.orm.session import _state_session
from sqlalchemy.util import set_creation_order
from sqlalchemy_utils.functions import identity
from .exceptions import ImproperlyConfigured
class GenericAttributeImpl(attributes.ScalarAttributeImpl):
def get(self, state, dict_, passive=attributes.PASSIVE_OFF):
if self.key in dict_:
return dict_[self.key]
# Retrieve the session bound to the state in order to perform
# a lazy query for the attribute.
session = _state_session(state)
if session is None:
# State is not bound to a session; we cannot proceed.
return None
# Find class for discriminator.
# TODO: Perhaps optimize with some sort of lookup?
discriminator = self.get_state_discriminator(state)
target_class = state.class_._decl_class_registry.get(discriminator)
if target_class is None:
# Unknown discriminator; return nothing.
return None
id = self.get_state_id(state)
target = session.query(target_class).get(id)
# Return found (or not found) target.
return target
def get_state_discriminator(self, state):
discriminator = self.parent_token.discriminator
if isinstance(discriminator, hybrid_property):
return getattr(state.obj(), discriminator.__name__)
else:
return state.attrs[discriminator.key].value
def get_state_id(self, state):
# Lookup row with the discriminator and id.
return tuple(state.attrs[id.key].value for id in self.parent_token.id)
def set(self, state, dict_, initiator,
passive=attributes.PASSIVE_OFF,
check_old=None,
pop=False):
# Set us on the state.
dict_[self.key] = initiator
if initiator is None:
# Nullify relationship args
for id in self.parent_token.id:
dict_[id.key] = None
dict_[self.parent_token.discriminator.key] = None
else:
# Get the primary key of the initiator and ensure we
# can support this assignment.
class_ = type(initiator)
mapper = class_mapper(class_)
pk = mapper.identity_key_from_instance(initiator)[1]
# Set the identifier and the discriminator.
discriminator = six.text_type(class_.__name__)
for index, id in enumerate(self.parent_token.id):
dict_[id.key] = pk[index]
dict_[self.parent_token.discriminator.key] = discriminator
class GenericRelationshipProperty(MapperProperty):
"""A generic form of the relationship property.
Creates a 1 to many relationship between the parent model
and any other models using a descriminator (the table name).
:param discriminator
Field to discriminate which model we are referring to.
:param id:
Field to point to the model we are referring to.
"""
def __init__(self, discriminator, id, doc=None):
super(GenericRelationshipProperty, self).__init__()
self._discriminator_col = discriminator
self._id_cols = id
self._id = None
self._discriminator = None
self.doc = doc
set_creation_order(self)
def _column_to_property(self, column):
if isinstance(column, hybrid_property):
attr_key = column.__name__
for key, attr in self.parent.all_orm_descriptors.items():
if key == attr_key:
return attr
else:
for key, attr in self.parent.attrs.items():
if isinstance(attr, ColumnProperty):
if attr.columns[0].name == column.name:
return attr
def init(self):
def convert_strings(column):
if isinstance(column, six.string_types):
return self.parent.columns[column]
return column
self._discriminator_col = convert_strings(self._discriminator_col)
self._id_cols = convert_strings(self._id_cols)
if isinstance(self._id_cols, Iterable):
self._id_cols = list(map(convert_strings, self._id_cols))
else:
self._id_cols = [self._id_cols]
self.discriminator = self._column_to_property(self._discriminator_col)
if self.discriminator is None:
raise ImproperlyConfigured(
'Could not find discriminator descriptor.'
)
self.id = list(map(self._column_to_property, self._id_cols))
class Comparator(PropComparator):
def __init__(self, prop, parentmapper):
self.property = prop
self._parententity = parentmapper
def __eq__(self, other):
discriminator = six.text_type(type(other).__name__)
q = self.property._discriminator_col == discriminator
other_id = identity(other)
for index, id in enumerate(self.property._id_cols):
q &= id == other_id[index]
return q
def __ne__(self, other):
return ~(self == other)
def is_type(self, other):
mapper = sa.inspect(other)
# Iterate through the weak sequence in order to get the actual
# mappers
class_names = [six.text_type(other.__name__)]
class_names.extend([
six.text_type(submapper.class_.__name__)
for submapper in mapper._inheriting_mappers
])
return self.property._discriminator_col.in_(class_names)
def instrument_class(self, mapper):
attributes.register_attribute(
mapper.class_,
self.key,
comparator=self.Comparator(self, mapper),
parententity=mapper,
doc=self.doc,
impl_class=GenericAttributeImpl,
parent_token=self
)
def generic_relationship(*args, **kwargs):
return GenericRelationshipProperty(*args, **kwargs)
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