DatabaseSession wrapper for orm.Session

For DB connections that want to keep a session alive, there's a new
`DatabaseSession` class that holds a SQLAlchemy session inside and
offers methods similar to the `Database` class.

The `Database` moves to use the `DatabaseSession` to remove duplicated
code.

pfbudget/db/client.py

@@ -3,66 +3,64 @@ from sqlalchemy import Engine, create_engine, select
 from sqlalchemy.orm import Session, sessionmaker
 from typing import Any, Optional, Sequence, Type, TypeVar
 
-from pfbudget.db.exceptions import InsertError, SelectError
+# from pfbudget.db.exceptions import InsertError, SelectError
 from pfbudget.db.model import Transaction
 
 
+class DatabaseSession:
+    def __init__(self, session: Session):
+        self.__session = session
+
+    def __enter__(self):
+        self.__session.begin()
+        return self
+
+    def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any):
+        if exc_type:
+            self.__session.rollback()
+        else:
+            self.__session.commit()
+        self.__session.close()
+
+    def insert(self, transactions: Sequence[Transaction]) -> None:
+        self.__session.add_all(transactions)
+
+    T = TypeVar("T")
+    C = TypeVar("C")
+
+    def select(self, what: Type[T], exists: Optional[Type[C]] = None) -> Sequence[T]:
+        if exists:
+            stmt = select(what).where(exists)
+        else:
+            stmt = select(what)
+
+        return self.__session.scalars(stmt).all()
+
+
 class Client:
-    def __init__(self, url: str, **kwargs: Any) -> None:
+    def __init__(self, url: str, **kwargs: Any):
         assert url, "Database URL is empty!"
         self._engine = create_engine(url, **kwargs)
         self._sessionmaker: Optional[sessionmaker[Session]] = None
 
-    def insert(
-        self, transactions: Sequence[Transaction], session: Optional[Session] = None
-    ) -> None:
-        if not session:
-            new = deepcopy(transactions)
-            with self.session as session_:
-                try:
-                    session_.add_all(new)
-                except Exception as e:
-                    session_.rollback()
-                    raise InsertError(e)
-                else:
-                    session_.commit()
-        else:
-            try:
-                session.add_all(transactions)
-            except Exception as e:
-                session.rollback()
-                raise InsertError(e)
-            else:
-                session.commit()
+    def insert(self, transactions: Sequence[Transaction]) -> None:
+        new = deepcopy(transactions)
+        with self.session as session:
+            session.insert(new)
 
     T = TypeVar("T")
+    C = TypeVar("C")
 
-    def select(self, what: Type[T], session: Optional[Session] = None) -> Sequence[T]:
-        stmt = select(what)
-        result: Sequence[what] = []
-
-        if not session:
-            with self.session as session_:
-                try:
-                    result = session_.scalars(stmt).all()
-                except Exception as e:
-                    session_.rollback()
-                    raise SelectError(e)
-        else:
-            try:
-                result = session.scalars(stmt).all()
-            except Exception as e:
-                session.rollback()
-                raise SelectError(e)
-
-        return result
+    def select(self, what: Type[T], exists: Optional[Type[C]] = None) -> Sequence[T]:
+        return self.session.select(what, exists)
 
     @property
     def engine(self) -> Engine:
         return self._engine
 
     @property
-    def session(self) -> Session:
+    def session(self) -> DatabaseSession:
         if not self._sessionmaker:
             self._sessionmaker = sessionmaker(self._engine)
-        return self._sessionmaker()
+
+        return DatabaseSession(self._sessionmaker())

tests/test_database.py

@@ -25,8 +25,8 @@ class TestDatabase:
         ]
 
         with client.session as session:
-            client.insert(transactions, session)
-            assert client.select(Transaction, session) == transactions
+            session.insert(transactions)
+            assert session.select(Transaction) == transactions
 
     def test_insert_transactions_independent_sessions(self, client: Client):
         transactions = [