Function load_name_range

examples/dogpile_caching/advanced.py:16–57

Load Person objects on a range of names. start/end are integers, range is then "person <start>" - "person <end>". The cache option we set up is called "name_range", indicating a range of names for the Person class. The `Person.addresses` collections are also cached. Its basic

(start, end, invalidate=False)

def load_name_range(start, end, invalidate=False):
    """Load Person objects on a range of names.

    start/end are integers, range is then
    "person <start>" - "person <end>".

    The cache option we set up is called "name_range", indicating
    a range of names for the Person class.

    The `Person.addresses` collections are also cached.  Its basically
    another level of tuning here, as that particular cache option
    can be transparently replaced with joinedload(Person.addresses).
    The effect is that each Person and their Address collection
    is cached either together or separately, affecting the kind of
    SQL that emits for unloaded Person objects as well as the distribution
    of data within the cache.
    """
    q = (
        select(Person)
        .filter(
            Person.name.between("person %.2d" % start, "person %.2d" % end)
        )
        .options(cache_address_bits)
        .options(FromCache("default", "name_range"))
    )

    # have the "addresses" collection cached separately
    # each lazyload of Person.addresses loads from cache.
    q = q.options(RelationshipCache(Person.addresses, "default"))

    # alternatively, eagerly load the "addresses" collection, so that they'd
    # be cached together.   This issues a bigger SQL statement and caches
    # a single, larger value in the cache per person rather than two
    # separate ones.
    # q = q.options(joinedload(Person.addresses))

    # if requested, invalidate the cache on current criterion.
    if invalidate:
        cache.invalidate(q, {}, FromCache("default", "name_range"))
        cache.invalidate(q, {}, RelationshipCache(Person.addresses, "default"))

    return Session.scalars(q).all()


print("two through twelve, possibly from cache:\n")