+class PlaceFetcher:
+ """ Asynchronous connection that fetches place details for processing.
+ """
+ def __init__(self, dsn, setup_conn):
+ self.wait_time = 0
+ self.current_ids = None
+ self.conn = DBConnection(dsn, cursor_factory=psycopg2.extras.DictCursor)
+
+ with setup_conn.cursor() as cur:
+ # need to fetch those manually because register_hstore cannot
+ # fetch them on an asynchronous connection below.
+ hstore_oid = cur.scalar("SELECT 'hstore'::regtype::oid")
+ hstore_array_oid = cur.scalar("SELECT 'hstore[]'::regtype::oid")
+
+ psycopg2.extras.register_hstore(self.conn.conn, oid=hstore_oid,
+ array_oid=hstore_array_oid)
+
+ def close(self):
+ """ Close the underlying asynchronous connection.
+ """
+ if self.conn:
+ self.conn.close()
+ self.conn = None
+
+
+ def fetch_next_batch(self, cur, runner):
+ """ Send a request for the next batch of places.
+ If details for the places are required, they will be fetched
+ asynchronously.
+
+ Returns true if there is still data available.
+ """
+ ids = cur.fetchmany(100)
+
+ if not ids:
+ self.current_ids = None
+ return False
+
+ if hasattr(runner, 'get_place_details'):
+ runner.get_place_details(self.conn, ids)
+ self.current_ids = []
+ else:
+ self.current_ids = ids
+
+ return True
+
+ def get_batch(self):
+ """ Get the next batch of data, previously requested with
+ `fetch_next_batch`.
+ """
+ if self.current_ids is not None and not self.current_ids:
+ tstart = time.time()
+ self.conn.wait()
+ self.wait_time += time.time() - tstart
+ self.current_ids = self.conn.cursor.fetchall()
+
+ return self.current_ids
+
+ def __enter__(self):
+ return self
+
+
+ def __exit__(self, exc_type, exc_value, traceback):
+ self.conn.wait()
+ self.close()