Implement migration script with ussd and notify

apps/cic-ussd/cic_ussd/db/models/base.py

@@ -1,47 +1,129 @@
-# standard imports
+# stanard imports
+import logging
 import datetime
 
-# third-party imports
+# external imports
 from sqlalchemy import Column, Integer, DateTime
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy import create_engine
 from sqlalchemy.orm import sessionmaker
+from sqlalchemy.pool import (
+        StaticPool,
+        QueuePool,
+        AssertionPool,
+        NullPool,
+        )
+
+logg = logging.getLogger().getChild(__name__)
 
 Model = declarative_base(name='Model')
 
 
 class SessionBase(Model):
+    """The base object for all SQLAlchemy enabled models. All other models must extend this.
+    """
     __abstract__ = True
 
-    id = Column(Integer, primary_key=True)
     created = Column(DateTime, default=datetime.datetime.utcnow)
     updated = Column(DateTime, default=datetime.datetime.utcnow, onupdate=datetime.datetime.utcnow)
 
+    id = Column(Integer, primary_key=True)
+
     engine = None
-    session = None
-    query = None
+    """Database connection engine of the running aplication"""
+    sessionmaker = None
+    """Factory object responsible for creating sessions from the  connection pool"""
+    transactional = True
+    """Whether the database backend supports query transactions. Should be explicitly set by initialization code"""
+    poolable = True
+    """Whether the database backend supports connection pools. Should be explicitly set by initialization code"""
+    procedural = True
+    """Whether the database backend supports stored procedures"""
+    localsessions = {}
+    """Contains dictionary of sessions initiated by db model components"""
+
 
     @staticmethod
     def create_session():
-        session = sessionmaker(bind=SessionBase.engine)
-        return session()
+        """Creates a new database session.
+        """
+        return SessionBase.sessionmaker()
+
 
     @staticmethod
     def _set_engine(engine):
+        """Sets the database engine static property
+        """
         SessionBase.engine = engine
+        SessionBase.sessionmaker = sessionmaker(bind=SessionBase.engine)
+
 
     @staticmethod
-    def build():
-        Model.metadata.create_all(bind=SessionBase.engine)
+    def connect(dsn, pool_size=16, debug=False):
+        """Create new database connection engine and connect to database backend.
+
+        :param dsn: DSN string defining connection.
+        :type dsn: str
+        """
+        e = None
+        if SessionBase.poolable:
+            poolclass = QueuePool
+            if pool_size > 1:
+                logg.info('db using queue pool')
+                e = create_engine(
+                        dsn,
+                        max_overflow=pool_size*3,
+                        pool_pre_ping=True,
+                        pool_size=pool_size,
+                        pool_recycle=60,
+                        poolclass=poolclass,
+                        echo=debug,
+                    )
+            else:
+                if pool_size == 0:
+                    poolclass = NullPool
+                elif debug:
+                    poolclass = AssertionPool
+                else:
+                    poolclass = StaticPool
+                e = create_engine(
+                        dsn,
+                        poolclass=poolclass,
+                        echo=debug,
+                    )
+        else:
+            logg.info('db connection not poolable')
+            e = create_engine(
+                    dsn,
+                    echo=debug,
+                    )
+
+        SessionBase._set_engine(e)
 
-    @staticmethod
-    # https://docs.sqlalchemy.org/en/13/core/pooling.html#pool-disconnects
-    def connect(data_source_name):
-        engine = create_engine(data_source_name, pool_pre_ping=True)
-        SessionBase._set_engine(engine)
 
     @staticmethod
     def disconnect():
+        """Disconnect from database and free resources.
+        """
         SessionBase.engine.dispose()
         SessionBase.engine = None
 
+
+    @staticmethod
+    def bind_session(session=None):
+        localsession = session
+        if localsession == None:
+            localsession = SessionBase.create_session()
+            localsession_key = str(id(localsession))
+            logg.debug('creating new session {}'.format(localsession_key))
+            SessionBase.localsessions[localsession_key] = localsession
+        return localsession
+
+
+    @staticmethod
+    def release_session(session=None):
+        session_key = str(id(session))
+        if SessionBase.localsessions.get(session_key) != None:
+            logg.debug('commit and destroy session {}'.format(session_key))
+            session.commit()
+            session.close()