examples.dogpile_caching.advanced
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2023-12-01
"""Illustrate usage of Query combined with the FromCache option, including front-end loading, cache invalidation and collection caching. """ from .caching_query import FromCache from .caching_query import RelationshipCache from .environment import cache from .environment import Session from .model import cache_address_bits from .model import Person 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 = ( Session.query(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 q.all() print("two through twelve, possibly from cache:\n") print(", ".join([p.name for p in load_name_range(2, 12)])) print("\ntwenty five through forty, possibly from cache:\n") print(", ".join([p.name for p in load_name_range(25, 40)])) # loading them again, no SQL is emitted print("\ntwo through twelve, from the cache:\n") print(", ".join([p.name for p in load_name_range(2, 12)])) # but with invalidate, they are print("\ntwenty five through forty, invalidate first:\n") print(", ".join([p.name for p in load_name_range(25, 40, True)])) # illustrate the address loading from either cache/already # on the Person print( "\n\nPeople plus addresses, two through twelve, addresses " "possibly from cache" ) for p in load_name_range(2, 12): print(p.format_full()) # illustrate the address loading from either cache/already # on the Person print("\n\nPeople plus addresses, two through twelve, addresses from cache") for p in load_name_range(2, 12): print(p.format_full()) print( "\n\nIf this was the first run of advanced.py, try " "a second run. Only one SQL statement will be emitted." )