finally properly handle transactions

app/db.py

@@ -5,10 +5,11 @@ from flask import current_app
 class DB:
     def __init__(self):
         self._connection = None
+        self._transaction_depth = 0
 
 
     @contextmanager
-    def _get_connection(self):
+    def connection(self, in_transaction = False):
         if self._connection:
             yield self._connection
             return
@@ -18,29 +19,36 @@ class DB:
         conn.execute("PRAGMA FOREIGN_KEYS = 1")
 
         try:
+            if in_transaction:
+                self._connection = conn
+                self._transaction_depth += 1
+                conn.execute("BEGIN")
+
             yield conn
+
+            if in_transaction:
+                conn.commit()
+        except Exception:
+            if in_transaction and self._connection:
+                conn.rollback()
         finally:
+            if in_transaction:
+                self._transaction_depth -= 1
+                if self._transaction_depth == 0:
+                    self._connection = None
                     conn.close()
 
 
     @contextmanager
     def transaction(self):
         """Transaction context."""
-        tr_connection = sqlite3.connect(current_app.config["DB_PATH"])
+        with self.connection(in_transaction=True) as conn:
-        tr_connection.row_factory = sqlite3.Row
+            yield conn
-        tr_connection.execute("PRAGMA FOREIGN_KEYS = 1")
-        tr_connection.execute("BEGIN")
-        try:
-            yield
-            tr_connection.execute("COMMIT")
-        except Exception:
-            tr_connection.execute("ROLLBACK")
-            raise
 
 
     def query(self, sql, *args):
         """Executes a query and returns a list of dictionaries."""
-        with self._get_connection() as conn:
+        with self.connection() as conn:
             rows = conn.execute(sql, args).fetchall()
             return [dict(row) for row in rows]
 
@@ -56,7 +64,7 @@ class DB:
             RETURNING *
         """
 
-        with self._get_connection() as conn:
+        with self.connection() as conn:
             result = conn.execute(sql, values).fetchone()
             conn.commit()
             return dict(result) if result else None
@@ -64,14 +72,14 @@ class DB:
 
     def execute(self, sql, *args):
         """Executes a query without returning."""
-        with self._get_connection() as conn:
+        with self.connection() as conn:
             conn.execute(sql, args)
             conn.commit()
 
 
     def fetch_one(self, sql, *args):
         """Grabs the first row of a query."""
-        with self._get_connection() as conn:
+        with self.connection() as conn:
             row = conn.execute(sql, args).fetchone()
             return dict(row) if row else None