examples.dogpile_caching.helloworld — SQLAlchemy 2.0 Documentation

Release: 2.0.49 | Release Date: April 3, 2026

# SQLAlchemy 2.0 Documentation

# Source code for examples.dogpile_caching.helloworld

    """Illustrate how to load some data, and cache the results."""

    from sqlalchemy import select
    from .caching_query import FromCache
    from .environment import cache
    from .environment import Session
    from .model import Person

    # load Person objects.  cache the result in the "default" cache region
    print("loading people....")
    people = Session.scalars(select(Person).options(FromCache("default"))).all()

    # remove the Session.  next query starts from scratch.
    Session.remove()

    # load again, using the same FromCache option. now they're cached,
    # so no SQL is emitted.
    print("loading people....again!")
    people = Session.scalars(select(Person).options(FromCache("default"))).all()

    # Specifying a different query produces a different cache key, so
    # these results are independently cached.
    print("loading people two through twelve")
    people_two_through_twelve = Session.scalars(
        select(Person)
        .options(FromCache("default"))
        .filter(Person.name.between("person 02", "person 12"))
    ).all()

    # the data is cached under string structure of the SQL statement, *plus*
    # the bind parameters of the query.    So this query, having
    # different literal parameters under "Person.name.between()" than the
    # previous one, issues new SQL...
    print("loading people five through fifteen")
    people_five_through_fifteen = Session.scalars(
        select(Person)
        .options(FromCache("default"))
        .filter(Person.name.between("person 05", "person 15"))
    ).all()

    # ... but using the same params as are already cached, no SQL
    print("loading people two through twelve...again!")
    people_two_through_twelve = Session.scalars(
        select(Person)
        .options(FromCache("default"))
        .filter(Person.name.between("person 02", "person 12"))
    ).all()

    # invalidate the cache for the three queries we've done.  Recreate
    # each Query, which includes at the very least the same FromCache,
    # same list of objects to be loaded, and the same parameters in the
    # same order, then call invalidate().
    print("invalidating everything")

    cache.invalidate(Session.query(Person), {}, FromCache("default"))
    cache.invalidate(
        select(Person).filter(Person.name.between("person 02", "person 12")),
        {},
        FromCache("default"),
    )
    cache.invalidate(
        select(Person).filter(Person.name.between("person 05", "person 15")),
        {},
        FromCache("default", "people_on_range"),
    )