SQLAlchemy 版本控制关注类导入顺序

"""Stolen from the offical sqlalchemy recpies
"""
from sqlalchemy.ext.declarative import DeclarativeMeta
from sqlalchemy.orm import mapper, class_mapper, attributes, object_mapper
from sqlalchemy.orm.exc import UnmappedClassError, UnmappedColumnError
from sqlalchemy import Table, Column, ForeignKeyConstraint, Integer
from sqlalchemy.orm.interfaces import SessionExtension
from sqlalchemy.orm.properties import RelationshipProperty
from sqlalchemy.types import DateTime
import datetime
from sqlalchemy.orm.session import Session


def col_references_table(col, table):
for fk in col.foreign_keys:
if fk.references(table):
return True
return False


def _history_mapper(local_mapper):
cls = local_mapper.class_


# set the "active_history" flag
# on on column-mapped attributes so that the old version
# of the info is always loaded (currently sets it on all attributes)
for prop in local_mapper.iterate_properties:
getattr(local_mapper.class_, prop.key).impl.active_history = True


super_mapper = local_mapper.inherits
super_history_mapper = getattr(cls, '__history_mapper__', None)


polymorphic_on = None
super_fks = []
if not super_mapper or local_mapper.local_table is not super_mapper.local_table:
cols = []
for column in local_mapper.local_table.c:
if column.name == 'version':
continue


col = column.copy()
col.unique = False


#don't auto increment stuff from the normal db
if col.autoincrement:
col.autoincrement = False
#sqllite falls over with auto incrementing keys if we have a composite key
if col.primary_key:
col.primary_key = False


if super_mapper and col_references_table(column, super_mapper.local_table):
super_fks.append((col.key, list(super_history_mapper.base_mapper.local_table.primary_key)[0]))


cols.append(col)


if column is local_mapper.polymorphic_on:
polymorphic_on = col


#if super_mapper:
#    super_fks.append(('version', super_history_mapper.base_mapper.local_table.c.version))


cols.append(Column('hist_id', Integer, primary_key=True, autoincrement=True))
cols.append(Column('version', Integer))
cols.append(Column('changed', DateTime, default=datetime.datetime.now))


if super_fks:
cols.append(ForeignKeyConstraint(*zip(*super_fks)))


table = Table(local_mapper.local_table.name + '_history', local_mapper.local_table.metadata,
*cols, mysql_engine='InnoDB')
else:
# single table inheritance.  take any additional columns that may have
# been added and add them to the history table.
for column in local_mapper.local_table.c:
if column.key not in super_history_mapper.local_table.c:
col = column.copy()
super_history_mapper.local_table.append_column(col)
table = None


if super_history_mapper:
bases = (super_history_mapper.class_,)
else:
bases = local_mapper.base_mapper.class_.__bases__
versioned_cls = type.__new__(type, "%sHistory" % cls.__name__, bases, {})


m = mapper(
versioned_cls,
table,
inherits=super_history_mapper,
polymorphic_on=polymorphic_on,
polymorphic_identity=local_mapper.polymorphic_identity
)
cls.__history_mapper__ = m


if not super_history_mapper:
cls.version = Column('version', Integer, default=1, nullable=False)


create_mappers = []


class VersionedMeta(DeclarativeMeta):
def __init__(cls, classname, bases, dict_):
DeclarativeMeta.__init__(cls, classname, bases, dict_)
#I added this code in as it was crashing otherwise
def make_mapper():
try:
mapper = class_mapper(cls)
_history_mapper(mapper)
except UnmappedClassError:
pass


create_mappers.append(lambda: make_mapper())


def versioned_objects(iter):
for obj in iter:
if hasattr(obj, '__history_mapper__'):
yield obj


def create_version(obj, session, deleted = False):
obj_mapper = object_mapper(obj)
history_mapper = obj.__history_mapper__
history_cls = history_mapper.class_


obj_state = attributes.instance_state(obj)


attr = {}


obj_changed = False


for om, hm in zip(obj_mapper.iterate_to_root(), history_mapper.iterate_to_root()):
if hm.single:
continue


for hist_col in hm.local_table.c:
if hist_col.key == 'version' or hist_col.key == 'changed' or hist_col.key == 'hist_id':
continue


obj_col = om.local_table.c[hist_col.key]


# get the value of the
# attribute based on the MapperProperty related to the
# mapped column.  this will allow usage of MapperProperties
# that have a different keyname than that of the mapped column.
try:
prop = obj_mapper.get_property_by_column(obj_col)
except UnmappedColumnError:
# in the case of single table inheritance, there may be
# columns on the mapped table intended for the subclass only.
# the "unmapped" status of the subclass column on the
# base class is a feature of the declarative module as of sqla 0.5.2.
continue


# expired object attributes and also deferred cols might not be in the
# dict.  force it to load no matter what by using getattr().
if prop.key not in obj_state.dict:
getattr(obj, prop.key)


a, u, d = attributes.get_history(obj, prop.key)


if d:
attr[hist_col.key] = d[0]
obj_changed = True
elif u:
attr[hist_col.key] = u[0]
else:
# if the attribute had no value.
attr[hist_col.key] = a[0]
obj_changed = True


if not obj_changed:
# not changed, but we have relationships.  OK
# check those too
for prop in obj_mapper.iterate_properties:
if isinstance(prop, RelationshipProperty) and \
attributes.get_history(obj, prop.key).has_changes():
obj_changed = True
break


if not obj_changed and not deleted:
return


attr['version'] = obj.version
hist = history_cls()
for key, value in attr.iteritems():
setattr(hist, key, value)


obj.version += 1
session.add(hist)


class VersionedListener(SessionExtension):
def before_flush(self, session, flush_context, instances):
for obj in versioned_objects(session.dirty):
create_version(obj, session)
for obj in versioned_objects(session.deleted):
create_version(obj, session, deleted = True)