import sqlalchemy as sa
from .exceptions import ImproperlyConfigured
def coercion_listener(mapper, class_):
"""
Auto assigns coercing listener for all class properties which are of coerce
capable type.
"""
for prop in mapper.iterate_properties:
try:
listener = prop.columns[0].type.coercion_listener
except AttributeError:
continue
sa.event.listen(
getattr(class_, prop.key),
'set',
listener,
retval=True
)
def instant_defaults_listener(target, args, kwargs):
# insertion order of kwargs matters
# copy and clear so that we can add back later at the end of the dict
original = kwargs.copy()
kwargs.clear()
for key, column in sa.inspect(target.__class__).columns.items():
if (
hasattr(column, 'default') and
column.default is not None
):
if callable(column.default.arg):
kwargs[key] = column.default.arg(target)
else:
kwargs[key] = column.default.arg
# supersede w/initial in case target uses setters overriding defaults
kwargs.update(original)
[docs]def force_auto_coercion(mapper=None):
"""
Function that assigns automatic data type coercion for all classes which
are of type of given mapper. The coercion is applied to all coercion
capable properties. By default coercion is applied to all SQLAlchemy
mappers.
Before initializing your models you need to call force_auto_coercion.
::
from sqlalchemy_utils import force_auto_coercion
force_auto_coercion()
Then define your models the usual way::
class Document(Base):
__tablename__ = 'document'
id = sa.Column(sa.Integer, autoincrement=True)
name = sa.Column(sa.Unicode(50))
background_color = sa.Column(ColorType)
Now scalar values for coercion capable data types will convert to
appropriate value objects::
document = Document()
document.background_color = 'F5F5F5'
document.background_color # Color object
session.commit()
A useful side effect of this is that additional validation of data will be
done on the moment it is being assigned to model objects. For example
without autocorrection set, an invalid
:class:`sqlalchemy_utils.types.IPAddressType` (eg. ``10.0.0 255.255``)
would get through without an exception being raised. The database wouldn't
notice this (as most databases don't have a native type for an IP address,
so they're usually just stored as a string), and the ``ipaddress``
package uses a string field as well.
:param mapper: The mapper which the automatic data type coercion should be
applied to
"""
if mapper is None:
mapper = sa.orm.Mapper
sa.event.listen(mapper, 'mapper_configured', coercion_listener)
[docs]def force_instant_defaults(mapper=None):
"""
Function that assigns object column defaults on object initialization
time. By default calling this function applies instant defaults to all
your models.
Setting up instant defaults::
from sqlalchemy_utils import force_instant_defaults
force_instant_defaults()
Example usage::
class Document(Base):
__tablename__ = 'document'
id = sa.Column(sa.Integer, autoincrement=True)
name = sa.Column(sa.Unicode(50))
created_at = sa.Column(sa.DateTime, default=datetime.now)
document = Document()
document.created_at # datetime object
:param mapper: The mapper which the automatic instant defaults forcing
should be applied to
"""
if mapper is None:
mapper = sa.orm.Mapper
sa.event.listen(mapper, 'init', instant_defaults_listener)
[docs]def auto_delete_orphans(attr):
"""
Delete orphans for given SQLAlchemy model attribute. This function can be
used for deleting many-to-many associated orphans easily. For more
information see
https://bitbucket.org/zzzeek/sqlalchemy/wiki/UsageRecipes/ManyToManyOrphan.
Consider the following model definition:
::
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy import *
from sqlalchemy.orm import *
# Necessary in sqlalchemy 1.3:
# from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import event
Base = declarative_base()
tagging = Table(
'tagging',
Base.metadata,
Column(
'tag_id',
Integer,
ForeignKey('tag.id', ondelete='CASCADE'),
primary_key=True
),
Column(
'entry_id',
Integer,
ForeignKey('entry.id', ondelete='CASCADE'),
primary_key=True
)
)
class Tag(Base):
__tablename__ = 'tag'
id = Column(Integer, primary_key=True)
name = Column(String(100), unique=True, nullable=False)
def __init__(self, name=None):
self.name = name
class Entry(Base):
__tablename__ = 'entry'
id = Column(Integer, primary_key=True)
tags = relationship(
'Tag',
secondary=tagging,
backref='entries'
)
Now lets say we want to delete the tags if all their parents get deleted (
all Entry objects get deleted). This can be achieved as follows:
::
from sqlalchemy_utils import auto_delete_orphans
auto_delete_orphans(Entry.tags)
After we've set up this listener we can see it in action.
::
e = create_engine('sqlite://')
Base.metadata.create_all(e)
s = Session(e)
r1 = Entry()
r2 = Entry()
r3 = Entry()
t1, t2, t3, t4 = Tag('t1'), Tag('t2'), Tag('t3'), Tag('t4')
r1.tags.extend([t1, t2])
r2.tags.extend([t2, t3])
r3.tags.extend([t4])
s.add_all([r1, r2, r3])
assert s.query(Tag).count() == 4
r2.tags.remove(t2)
assert s.query(Tag).count() == 4
r1.tags.remove(t2)
assert s.query(Tag).count() == 3
r1.tags.remove(t1)
assert s.query(Tag).count() == 2
.. versionadded: 0.26.4
:param attr: Association relationship attribute to auto delete orphans from
"""
parent_class = attr.parent.class_
target_class = attr.property.mapper.class_
backref = attr.property.backref
if not backref:
raise ImproperlyConfigured(
'The relationship argument given for auto_delete_orphans needs to '
'have a backref relationship set.'
)
if isinstance(backref, tuple):
backref = backref[0]
@sa.event.listens_for(sa.orm.Session, 'after_flush')
def delete_orphan_listener(session, ctx):
# Look through Session state to see if we want to emit a DELETE for
# orphans
orphans_found = (
any(
isinstance(obj, parent_class) and
sa.orm.attributes.get_history(obj, attr.key).deleted
for obj in session.dirty
) or
any(
isinstance(obj, parent_class)
for obj in session.deleted
)
)
if orphans_found:
# Emit a DELETE for all orphans
(
session.query(target_class)
.filter(
~getattr(target_class, backref).any()
)
.delete(synchronize_session=False)
)