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"""Illustrates a custom per-query criteria that will be applied
to selected entities.
"""
import datetime
from sqlalchemy import Column
from sqlalchemy import DateTime
from sqlalchemy import orm
class HasTemporal(object):
"""Mixin that identifies a class as having a timestamp column"""
timestamp = Column(
DateTime, default=datetime.datetime.utcnow, nullable=False
)
def temporal_range(range_lower, range_upper):
return orm.with_loader_criteria(
HasTemporal,
lambda cls: cls.timestamp.between(range_lower, range_upper),
include_aliases=True,
)
if __name__ == "__main__":
from sqlalchemy import Integer, Column, ForeignKey
from sqlalchemy import select
from sqlalchemy import create_engine
from sqlalchemy.orm import relationship, sessionmaker, selectinload
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Parent(HasTemporal, Base):
__tablename__ = "parent"
id = Column(Integer, primary_key=True)
children = relationship("Child")
class Child(HasTemporal, Base):
__tablename__ = "child"
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey("parent.id"), nullable=False)
engine = create_engine("sqlite://", echo=True)
Base.metadata.create_all(engine)
Session = sessionmaker(bind=engine, future=True)
sess = Session()
c1, c2, c3, c4, c5 = [
Child(timestamp=datetime.datetime(2009, 10, 15, 12, 00, 00)),
Child(timestamp=datetime.datetime(2009, 10, 17, 12, 00, 00)),
Child(timestamp=datetime.datetime(2009, 10, 20, 12, 00, 00)),
Child(timestamp=datetime.datetime(2009, 10, 12, 12, 00, 00)),
Child(timestamp=datetime.datetime(2009, 10, 17, 12, 00, 00)),
]
p1 = Parent(
timestamp=datetime.datetime(2009, 10, 15, 12, 00, 00),
children=[c1, c2, c3],
)
p2 = Parent(
timestamp=datetime.datetime(2009, 10, 17, 12, 00, 00),
children=[c4, c5],
)
sess.add_all([p1, p2])
sess.commit()
# use populate_existing() to ensure the range option takes
# place for elements already in the identity map
parents = (
sess.query(Parent)
.populate_existing()
.options(
temporal_range(
datetime.datetime(2009, 10, 16, 12, 00, 00),
datetime.datetime(2009, 10, 18, 12, 00, 00),
)
)
.all()
)
assert parents[0] == p2
assert parents[0].children == [c5]
sess.expire_all()
# try it with eager load
parents = (
sess.query(Parent)
.options(
temporal_range(
datetime.datetime(2009, 10, 16, 12, 00, 00),
datetime.datetime(2009, 10, 18, 12, 00, 00),
)
)
.options(selectinload(Parent.children))
.all()
)
assert parents[0] == p2
assert parents[0].children == [c5]
sess.expire_all()
# illustrate a 2.0 style query
print("------------------")
parents = (
sess.execute(
select(Parent)
.execution_options(populate_existing=True)
.options(
temporal_range(
datetime.datetime(2009, 10, 15, 11, 00, 00),
datetime.datetime(2009, 10, 18, 12, 00, 00),
)
)
.join(Parent.children)
.filter(Child.id == 2)
)
.scalars()
.all()
)
assert parents[0] == p1
print("-------------------")
assert parents[0].children == [c1, c2]
|
