"""Versioned mixin class and other utilities."""
import datetime
from sqlalchemy import Column
from sqlalchemy import DateTime
from sqlalchemy import event
from sqlalchemy import ForeignKeyConstraint
from sqlalchemy import inspect
from sqlalchemy import Integer
from sqlalchemy import PrimaryKeyConstraint
from sqlalchemy import util
from sqlalchemy.orm import attributes
from sqlalchemy.orm import object_mapper
from sqlalchemy.orm.exc import UnmappedColumnError
from sqlalchemy.orm.relationships import RelationshipProperty
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_
if cls.__dict__.get("_history_mapper_configured", False):
return
cls._history_mapper_configured = True
super_mapper = local_mapper.inherits
polymorphic_on = None
super_fks = []
properties = util.OrderedDict()
if super_mapper:
super_history_mapper = super_mapper.class_.__history_mapper__
else:
super_history_mapper = None
if (
not super_mapper
or local_mapper.local_table is not super_mapper.local_table
):
version_meta = {"version_meta": True} # add column.info to identify
# columns specific to versioning
history_table = local_mapper.local_table.to_metadata(
local_mapper.local_table.metadata,
name=local_mapper.local_table.name + "_history",
)
for orig_c, history_c in zip(
local_mapper.local_table.c, history_table.c
):
orig_c.info["history_copy"] = history_c
history_c.unique = False
history_c.default = history_c.server_default = None
history_c.autoincrement = False
if super_mapper and col_references_table(
orig_c, super_mapper.local_table
):
assert super_history_mapper is not None
super_fks.append(
(
history_c.key,
list(super_history_mapper.local_table.primary_key)[0],
)
)
if orig_c is local_mapper.polymorphic_on:
polymorphic_on = history_c
orig_prop = local_mapper.get_property_by_column(orig_c)
# carry over column re-mappings
if (
len(orig_prop.columns) > 1
or orig_prop.columns[0].key != orig_prop.key
):
properties[orig_prop.key] = tuple(
col.info["history_copy"] for col in orig_prop.columns
)
for const in list(history_table.constraints):
if not isinstance(
const, (PrimaryKeyConstraint, ForeignKeyConstraint)
):
history_table.constraints.discard(const)
# "version" stores the integer version id. This column is
# required.
history_table.append_column(
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.
history_table.append_column(
Column(
"changed",
DateTime,
default=lambda: datetime.datetime.now(datetime.timezone.utc),
info=version_meta,
)
)
if super_mapper:
super_fks.append(
("version", super_history_mapper.local_table.c.version)
)
if super_fks:
history_table.append_constraint(
ForeignKeyConstraint(*zip(*super_fks))
)
else:
history_table = None
super_history_table = super_mapper.local_table.metadata.tables[
super_mapper.local_table.name + "_history"
]
# 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_table.c:
col = Column(
column.name, column.type, nullable=column.nullable
)
super_history_table.append_column(col)
if not super_mapper:
local_mapper.local_table.append_column(
Column("version", Integer, default=1, nullable=False),
replace_existing=True,
)
local_mapper.add_property(
"version", local_mapper.local_table.c.version
)
if cls.use_mapper_versioning:
local_mapper.version_id_col = local_mapper.local_table.c.version
# 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:
prop.active_history = True
super_mapper = local_mapper.inherits
if super_history_mapper:
bases = (super_history_mapper.class_,)
if history_table is not None:
properties["changed"] = (history_table.c.changed,) + tuple(
super_history_mapper.attrs.changed.columns
)
else:
bases = local_mapper.base_mapper.class_.__bases__
versioned_cls = type(
"%sHistory" % cls.__name__,
bases,
{
"_history_mapper_configured": True,
"__table__": history_table,
"__mapper_args__": dict(
inherits=super_history_mapper,
polymorphic_identity=local_mapper.polymorphic_identity,
polymorphic_on=polymorphic_on,
properties=properties,
),
},
)
cls.__history_mapper__ = versioned_cls.__mapper__
class Versioned:
use_mapper_versioning = False
"""if True, also assign the version column to be tracked by the mapper"""
__table_args__ = {"sqlite_autoincrement": True}
"""Use sqlite_autoincrement, to ensure unique integer values
are used for new rows even for rows that have been deleted."""
def __init_subclass__(cls) -> None:
insp = inspect(cls, raiseerr=False)
if insp is not None:
_history_mapper(insp)
else:
@event.listens_for(cls, "after_mapper_constructed")
def _mapper_constructed(mapper, class_):
_history_mapper(mapper)
super().__init_subclass__()
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.
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[prop.key] = d[0]
obj_changed = True
elif u:
attr[prop.key] = u[0]
elif a:
# if the attribute had no value.
attr[prop.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)