chezbetty/models/history_meta.py
"""Versioned mixin class and other utilities."""
import datetime
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.orm import mapper, attributes, object_mapper
from sqlalchemy.orm.exc import UnmappedColumnError
from sqlalchemy import Table, Column, ForeignKeyConstraint, Integer, ForeignKey
from sqlalchemy import event
from sqlalchemy.orm.properties import RelationshipProperty
from sqlalchemy_utils import ArrowType
def col_references_table(col, table):
for fk in col.foreign_keys:
if fk.references(table):
return True
return False
def _is_versioning_col(col):
return "version_meta" in col.info
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 = []
def _col_copy(col):
col = col.copy()
col.unique = False
col.default = col.server_default = None
return col
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 _is_versioning_col(column):
continue
col = _col_copy(column)
if super_mapper and col_references_table(column, super_mapper.local_table):
super_fks.append((col.key, list(super_history_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.local_table.c.version))
version_meta = {"version_meta": True} # add column.info to identify
# columns specific to versioning
# "version" stores the integer version id. This column is
# required.
cols.append(Column('version', Integer, primary_key=True,
autoincrement=False, info=version_meta))
# "changed" column stores the UTC timestamp of when the
# history row was created.
# This column is optional and can be omitted.
model_name = cls.__name__.lower()
cols.append(Column('%s_changed_at' % model_name, ArrowType,
default=datetime.datetime.utcnow,
info=version_meta))
cols.append(Column('%s_changed_by' % model_name, Integer, ForeignKey("users.id"),
info=version_meta))
if super_fks:
cols.append(ForeignKeyConstraint(*zip(*super_fks)))
table = Table(local_mapper.local_table.name + '_history',
local_mapper.local_table.metadata,
*cols,
schema=local_mapper.local_table.schema
)
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 = _col_copy(column)
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:
local_mapper.local_table.append_column(
Column('version', Integer, default=1, nullable=False)
)
local_mapper.add_property("version", local_mapper.local_table.c.version)
class Versioned(object):
@declared_attr
def __mapper_cls__(cls):
def map(cls, *arg, **kw):
mp = mapper(cls, *arg, **kw)
_history_mapper(mp)
return mp
return map
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 _is_versioning_col(hist_col):
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,
passive=attributes.PASSIVE_NO_INITIALIZE).has_changes():
for p in prop.local_columns:
if p.foreign_keys:
obj_changed = True
break
if obj_changed is True:
break
if not obj_changed and not deleted:
return
attr['version'] = obj.version
hist = history_cls()
for key, value in attr.items():
setattr(hist, key, value)
session.add(hist)
obj.version += 1
def versioned_session(session):
@event.listens_for(session, 'before_flush')
def before_flush(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)
return session