examples.extending_query.temporal_range
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2023-12-01
"""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]