Removed connection.begin() pattern from the db plugin.

SQLAlchemy should automatically begin a transaction on
connection/session creation. Plus, `.begin()` messes up things with
SQLAlchemy 2, which has `autobegin` enabled with no easy way of
disabling it.

platypush/plugins/db/__init__.py

@@ -3,12 +3,7 @@ from contextlib import contextmanager
 from multiprocessing import RLock
 from typing import Optional, Generator, Union
 
-from sqlalchemy import (
-    create_engine,
-    Table,
-    MetaData,
-    __version__ as sa_version,
-)
+from sqlalchemy import create_engine, Table, MetaData
 from sqlalchemy.engine import Engine
 from sqlalchemy.exc import CompileError
 from sqlalchemy.orm import Session, sessionmaker, scoped_session
@@ -19,21 +14,6 @@ from platypush.plugins import Plugin, action
 session_locks = {}
 
 
-@contextmanager
-def conn_begin(conn):
-    """
-    Utility method to deal with `autobegin` being enabled on SQLAlchemy 2.0 but
-    not on earlier version.
-    """
-    sa_maj_ver = int(sa_version.split('.')[0])
-    if sa_maj_ver < 2:
-        yield conn.begin()
-    else:
-        yield conn._transaction
-
-    conn.commit()
-
-
 class DbPlugin(Plugin):
     """
     Database plugin. It allows you to programmatically select, insert, update
@@ -45,7 +25,7 @@ class DbPlugin(Plugin):
     _db_error_wait_interval = 5.0
     _db_error_retries = 3
 
-    def __init__(self, *args, engine=None, **kwargs):
+    def __init__(self, engine=None, **kwargs):
         """
         :param engine: Default SQLAlchemy connection engine string (e.g.
             ``sqlite:///:memory:`` or ``mysql://user:pass@localhost/test``)
@@ -62,7 +42,7 @@ class DbPlugin(Plugin):
 
         super().__init__()
         self.engine_url = engine
-        self.engine = self.get_engine(engine, *args, **kwargs)
+        self.engine = self.get_engine(engine, **kwargs)
 
     def get_engine(
         self, engine: Optional[Union[str, Engine]] = None, *args, **kwargs
@@ -116,12 +96,10 @@ class DbPlugin(Plugin):
             (see https:///docs.sqlalchemy.org/en/latest/core/engines.html)
         """
 
-        engine = self.get_engine(engine, *args, **kwargs)
-
-        with engine.connect() as connection:
+        with self.get_engine(engine, *args, **kwargs).connect() as connection:
             connection.execute(text(statement))
 
-    def _get_table(self, table: str, engine=None, *args, **kwargs):
+    def _get_table(self, table: str, *args, engine=None, **kwargs):
         if not engine:
             engine = self.get_engine(engine, *args, **kwargs)
 
@@ -344,7 +322,6 @@ class DbPlugin(Plugin):
                     connection, table, records, key_columns
                 )
 
-            with conn_begin(connection):
             if insert_records:
                 insert = table.insert().values(insert_records)
                 ret = self._execute_try_returning(connection, insert)
@@ -519,7 +496,7 @@ class DbPlugin(Plugin):
 
         engine = self.get_engine(engine, *args, **kwargs)
 
-        with engine.connect() as connection, conn_begin(connection):
+        with engine.connect() as connection:
             for record in records:
                 table_, engine = self._get_table(table, engine=engine, *args, **kwargs)
                 delete = table_.delete()
@@ -535,7 +512,7 @@ class DbPlugin(Plugin):
 
     @contextmanager
     def get_session(
-        self, engine=None, locked=False, autoflush=True, *args, **kwargs
+        self, *args, engine=None, locked=False, autoflush=True, **kwargs
     ) -> Generator[Session, None, None]:
         engine = self.get_engine(engine, *args, **kwargs)
         if locked:
@@ -544,16 +521,20 @@ class DbPlugin(Plugin):
             # Mock lock
             lock = RLock()
 
-        with lock, engine.connect() as conn, conn_begin(conn):
-            session = scoped_session(
+        with lock, engine.connect() as conn:
+            session_maker = scoped_session(
                 sessionmaker(
                     expire_on_commit=False,
                     autoflush=autoflush,
                 )
             )
 
-            session.configure(bind=conn)
-            yield session()
+            session_maker.configure(bind=conn)
+            session = session_maker()
+            yield session
+
+            session.flush()
+            session.commit()
 
 
 # vim:sw=4:ts=4:et: