From 9d8e9f891febf15aadc282200c689ddd1e2e3579 Mon Sep 17 00:00:00 2001
From: Shubha Rajan <shubhadayini@google.com>
Date: Tue, 28 Jun 2022 17:29:50 -0700
Subject: [PATCH] refactor DataAccessLayer class

---
 api/openapi_server/__main__.py                |  2 ++
 .../service_provider_controller.py            | 13 +++++-----
 api/openapi_server/models/database.py         | 24 ++++++++++++-------
 3 files changed, 23 insertions(+), 16 deletions(-)

diff --git a/api/openapi_server/__main__.py b/api/openapi_server/__main__.py
index 4dd755c5..0477888a 100644
--- a/api/openapi_server/__main__.py
+++ b/api/openapi_server/__main__.py
@@ -4,6 +4,7 @@
 from os import environ as env
 
 from openapi_server import encoder
+from openapi_server.models.database import DataAccessLayer
 from openapi_server.exceptions import AuthError, handle_auth_error
 from dotenv import load_dotenv, find_dotenv
 
@@ -13,6 +14,7 @@
     load_dotenv(ENV_FILE)
 SECRET_KEY=env.get('SECRET_KEY')
 
+DataAccessLayer.db_init()
 
 def main():
     app = connexion.App(__name__, specification_dir='./_spec/')
diff --git a/api/openapi_server/controllers/service_provider_controller.py b/api/openapi_server/controllers/service_provider_controller.py
index 40c2e37e..3d5b26fe 100644
--- a/api/openapi_server/controllers/service_provider_controller.py
+++ b/api/openapi_server/controllers/service_provider_controller.py
@@ -9,8 +9,7 @@
 from openapi_server.models import database as db
 from sqlalchemy.orm import Session
 
-dal = db.DataAccessLayer()
-dal.db_init()
+db_engine = db.DataAccessLayer.get_engine()
 
 def create_service_provider():  # noqa: E501
     """Create a housing program service provider
@@ -27,7 +26,7 @@ def create_service_provider():  # noqa: E501
                 connexion.request.get_json()).to_dict()  
         except ValueError:
             return traceback.format_exc(ValueError), 400
-        with Session(dal.engine) as session:
+        with Session(db_engine) as session:
             row = db.HousingProgramServiceProvider(
                 provider_name=provider["provider_name"]
             )
@@ -51,7 +50,7 @@ def delete_service_provider(provider_id):  # noqa: E501
 
     :rtype: None
     """
-    with Session(dal.engine) as session:
+    with Session(db_engine) as session:
         query = session.query(
                 db.HousingProgramServiceProvider).filter(
                     db.HousingProgramServiceProvider.id == provider_id)
@@ -71,7 +70,7 @@ def get_service_provider_by_id(provider_id):  # noqa: E501
 
     :rtype: ServiceProviderWithId
     """
-    with Session(dal.engine) as session:
+    with Session(db_engine) as session:
         row = session.get(
             db.HousingProgramServiceProvider, provider_id)
         if row != None:
@@ -93,7 +92,7 @@ def get_service_providers():  # noqa: E501
     :rtype: List[ServiceProviderWithId]
     """
     resp = []
-    with Session(dal.engine) as session:
+    with Session(db_engine) as session:
         table = session.query(db.HousingProgramServiceProvider).all()
         for row in table:
             provider = ServiceProvider(
@@ -122,7 +121,7 @@ def update_service_provider(provider_id):  # noqa: E501
                 connexion.request.get_json()).to_dict() 
         except ValueError:
             return traceback.format_exc(ValueError), 400
-        with Session(dal.engine) as session:
+        with Session(db_engine) as session:
             query = session.query(
                 db.HousingProgramServiceProvider).filter(
                     db.HousingProgramServiceProvider.id == provider_id)
diff --git a/api/openapi_server/models/database.py b/api/openapi_server/models/database.py
index 5077ff1c..becb01ff 100644
--- a/api/openapi_server/models/database.py
+++ b/api/openapi_server/models/database.py
@@ -233,16 +233,22 @@ class ProgramCaseStatusLog(Base):
     src_status = Column(Integer, ForeignKey('case_status.id'), nullable=False)
     dest_status = Column(Integer, ForeignKey('case_status.id'), nullable=False)
 
-
-
 class DataAccessLayer:
-    connection = None
-    engine = None
+    _engine = None
 
     # temporary local sqlite DB, replace with conn str for postgres container port for real e2e
-    conn_string = "sqlite:///./homeuniteus.db"
+    _conn_string = "sqlite:///./homeuniteus.db"
 
-    def db_init(self, conn_string=None):
-        self.engine = create_engine(conn_string or self.conn_string, echo=True, future=True) 
-        Base.metadata.create_all(bind=self.engine)
-        self.connection = self.engine.connect()
+    @classmethod
+    def db_init(cls, conn_string=None):
+        Base.metadata.create_all(bind=cls.get_engine(conn_string))
+    
+    @classmethod
+    def connect(cls):
+        return cls.get_engine().connect()
+    
+    @classmethod
+    def get_engine(cls, conn_string=None):
+        if cls._engine == None:
+            cls._engine = create_engine(conn_string or cls._conn_string, echo=True, future=True)
+        return cls._engine