mirror of https://github.com/ekimekim/wubloader
You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
98 lines
3.2 KiB
Python
98 lines
3.2 KiB
Python
|
|
"""
|
|
Code shared between components that touch the database.
|
|
Note that this code requires psycopg2 and psycogreen, but the common module
|
|
as a whole does not to avoid needing to install them for components that don't need it.
|
|
"""
|
|
|
|
from contextlib import contextmanager
|
|
|
|
import psycopg2
|
|
import psycopg2.sql
|
|
import psycopg2.extensions
|
|
import psycopg2.extras
|
|
from psycogreen.gevent import patch_psycopg
|
|
|
|
|
|
COMPOSITE_TYPES = [
|
|
"video_range",
|
|
"video_transition",
|
|
]
|
|
COLUMN_CASTS = {
|
|
"video_ranges": "video_range[]",
|
|
"video_transitions": "video_transition[]",
|
|
}
|
|
|
|
def get_column_placeholder(column):
|
|
"""Get a placeholder (like "%(COLUMN)s") to use in constructed SQL queries
|
|
for a given column in the events table. This function is needed because
|
|
some columns have types that require explicit casts to be included."""
|
|
placeholder = psycopg2.sql.Placeholder(column)
|
|
if column in COLUMN_CASTS:
|
|
placeholder = psycopg2.sql.SQL("{}::{}").format(
|
|
placeholder, psycopg2.sql.SQL(COLUMN_CASTS[column])
|
|
)
|
|
return placeholder
|
|
|
|
|
|
class DBManager(object):
|
|
"""Patches psycopg2 before any connections are created. Stores connect info
|
|
for easy creation of new connections, and sets some defaults before
|
|
returning them.
|
|
|
|
It has the ability to serve as a primitive connection pool, as getting a
|
|
new conn will return existing conns it knows about first, but you
|
|
should use a real conn pool for any non-trivial use.
|
|
|
|
Returned conns are set to seralizable isolation level, autocommit, and use
|
|
NamedTupleCursor cursors."""
|
|
def __init__(self, connect_timeout=30, **connect_kwargs):
|
|
patch_psycopg()
|
|
self.conns = []
|
|
self.connect_timeout = connect_timeout
|
|
self.connect_kwargs = connect_kwargs
|
|
|
|
def put_conn(self, conn):
|
|
self.conns.append(conn)
|
|
|
|
def get_conn(self):
|
|
if self.conns:
|
|
return self.conns.pop(0)
|
|
conn = psycopg2.connect(cursor_factory=psycopg2.extras.NamedTupleCursor,
|
|
connect_timeout=self.connect_timeout, **self.connect_kwargs)
|
|
# We use serializable because it means less issues to think about,
|
|
# we don't care about the performance concerns and everything we do is easily retryable.
|
|
# This shouldn't matter in practice anyway since everything we're doing is either read-only
|
|
# searches or targetted single-row updates.
|
|
conn.isolation_level = psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE
|
|
conn.autocommit = True
|
|
for composite in COMPOSITE_TYPES:
|
|
psycopg2.extras.register_composite(composite, conn)
|
|
return conn
|
|
|
|
|
|
@contextmanager
|
|
def transaction(conn):
|
|
"""Helper context manager that runs the code block as a single database transaction
|
|
instead of in autocommit mode. The only difference between this and "with conn" is
|
|
that we explicitly disable then re-enable autocommit."""
|
|
old_autocommit = conn.autocommit
|
|
conn.autocommit = False
|
|
try:
|
|
with conn:
|
|
yield
|
|
finally:
|
|
conn.autocommit = old_autocommit
|
|
|
|
|
|
def query(conn, query, *args, **kwargs):
|
|
"""Helper that takes a conn, creates a cursor and executes query against it,
|
|
then returns the cursor.
|
|
Variables may be given as positional or keyword args (but not both), corresponding
|
|
to %s vs %(key)s placeholder forms."""
|
|
if args and kwargs:
|
|
raise TypeError("Cannot give both args and kwargs")
|
|
cur = conn.cursor()
|
|
cur.execute(query, args or kwargs or None)
|
|
return cur
|