examples.dogpile_caching.helloworld — SQLAlchemy 1.2 Documentation

Release: 1.2.8 | Release Date: May 28, 2018

# SQLAlchemy 1.2 Documentation

# Source code for examples.dogpile_caching.helloworld

    """helloworld.py

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

    """

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

    # 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()