first commit

helix/db/sql_manager.py

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+import sqlalchemy
+from sqlalchemy.orm import sessionmaker
+
+
+class SQLManager(object):
+    # Cache the database connection per application process.
+    # More properly, this should be kept in thread-local state (threading.local()), but should suffice.
+    # Each passed connection url will have its own pool.
+    engines = {}
+
+    @classmethod
+    def get_sql_session_maker(cls, heroku_postgres_url, should_echo=False, cache=True):
+        if not cache:
+            return sessionmaker(bind=cls.connect(heroku_postgres_url, should_echo=should_echo))()
+        else:
+            engine = cls.engines.setdefault(heroku_postgres_url,
+                                            cls.connect(heroku_postgres_url, should_echo=should_echo))
+
+            return sessionmaker(bind=engine)()
+
+    @staticmethod
+    def connect(heroku_postgres_url, should_echo=False):
+        if heroku_postgres_url:
+            return sqlalchemy.create_engine(heroku_postgres_url, echo=should_echo)
+        else:
+            return sqlalchemy.create_engine('postgres://pivotal:@localhost/pivotal', echo=True)