Release: 1.3.3 current release | Release Date: April 15, 2019

SQLAlchemy 1.3 Documentation

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Source code for examples.dogpile_caching.helloworld

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

"""

from .caching_query import FromCache
from .environment import Session
from .model import Person


# load Person objects.  cache the result in the "default" cache region
print("loading people....")
people = Session.query(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.query(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.query(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.query(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.query(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")
Session.query(Person).options(FromCache("default")).invalidate()
Session.query(Person).options(FromCache("default")).filter(
    Person.name.between("person 02", "person 12")
).invalidate()
Session.query(Person).options(FromCache("default", "people_on_range")).filter(
    Person.name.between("person 05", "person 15")
).invalidate()