diff --git a/api/core/tools/workflow_as_tool/tool.py b/api/core/tools/workflow_as_tool/tool.py
index 81a1d54199..389db8a972 100644
--- a/api/core/tools/workflow_as_tool/tool.py
+++ b/api/core/tools/workflow_as_tool/tool.py
@@ -7,8 +7,8 @@ from typing import Any, cast
 
 from flask import has_request_context
 from sqlalchemy import select
-from sqlalchemy.orm import Session
 
+from core.db.session_factory import session_factory
 from core.file import FILE_MODEL_IDENTITY, File, FileTransferMethod
 from core.model_runtime.entities.llm_entities import LLMUsage, LLMUsageMetadata
 from core.tools.__base.tool import Tool
@@ -20,7 +20,6 @@ from core.tools.entities.tool_entities import (
     ToolProviderType,
 )
 from core.tools.errors import ToolInvokeError
-from extensions.ext_database import db
 from factories.file_factory import build_from_mapping
 from libs.login import current_user
 from models import Account, Tenant
@@ -230,30 +229,32 @@ class WorkflowTool(Tool):
         """
         Resolve user from database (worker/Celery context).
         """
+        with session_factory.create_session() as session:
+            tenant_stmt = select(Tenant).where(Tenant.id == self.runtime.tenant_id)
+            tenant = session.scalar(tenant_stmt)
+            if not tenant:
+                return None
+
+            user_stmt = select(Account).where(Account.id == user_id)
+            user = session.scalar(user_stmt)
+            if user:
+                user.current_tenant = tenant
+                session.expunge(user)
+                return user
+
+            end_user_stmt = select(EndUser).where(EndUser.id == user_id, EndUser.tenant_id == tenant.id)
+            end_user = session.scalar(end_user_stmt)
+            if end_user:
+                session.expunge(end_user)
+                return end_user
 
-        tenant_stmt = select(Tenant).where(Tenant.id == self.runtime.tenant_id)
-        tenant = db.session.scalar(tenant_stmt)
-        if not tenant:
             return None
 
-        user_stmt = select(Account).where(Account.id == user_id)
-        user = db.session.scalar(user_stmt)
-        if user:
-            user.current_tenant = tenant
-            return user
-
-        end_user_stmt = select(EndUser).where(EndUser.id == user_id, EndUser.tenant_id == tenant.id)
-        end_user = db.session.scalar(end_user_stmt)
-        if end_user:
-            return end_user
-
-        return None
-
     def _get_workflow(self, app_id: str, version: str) -> Workflow:
         """
         get the workflow by app id and version
         """
-        with Session(db.engine, expire_on_commit=False) as session, session.begin():
+        with session_factory.create_session() as session, session.begin():
             if not version:
                 stmt = (
                     select(Workflow)
@@ -265,22 +266,24 @@ class WorkflowTool(Tool):
                 stmt = select(Workflow).where(Workflow.app_id == app_id, Workflow.version == version)
                 workflow = session.scalar(stmt)
 
-        if not workflow:
-            raise ValueError("workflow not found or not published")
+            if not workflow:
+                raise ValueError("workflow not found or not published")
 
-        return workflow
+            session.expunge(workflow)
+            return workflow
 
     def _get_app(self, app_id: str) -> App:
         """
         get the app by app id
         """
         stmt = select(App).where(App.id == app_id)
-        with Session(db.engine, expire_on_commit=False) as session, session.begin():
+        with session_factory.create_session() as session, session.begin():
             app = session.scalar(stmt)
-        if not app:
-            raise ValueError("app not found")
+            if not app:
+                raise ValueError("app not found")
 
-        return app
+            session.expunge(app)
+            return app
 
     def _transform_args(self, tool_parameters: dict) -> tuple[dict, list[dict]]:
         """
diff --git a/api/tests/unit_tests/core/tools/workflow_as_tool/test_tool.py b/api/tests/unit_tests/core/tools/workflow_as_tool/test_tool.py
index 5d180c7cbc..cd45292488 100644
--- a/api/tests/unit_tests/core/tools/workflow_as_tool/test_tool.py
+++ b/api/tests/unit_tests/core/tools/workflow_as_tool/test_tool.py
@@ -228,11 +228,28 @@ def test_resolve_user_from_database_falls_back_to_end_user(monkeypatch: pytest.M
         def scalar(self, _stmt):
             return self.results.pop(0)
 
+        # SQLAlchemy Session APIs used by code under test
+        def expunge(self, *_args, **_kwargs):
+            pass
+
+        def close(self):
+            pass
+
+        # support `with session_factory.create_session() as session:`
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            self.close()
+
     tenant = SimpleNamespace(id="tenant_id")
     end_user = SimpleNamespace(id="end_user_id", tenant_id="tenant_id")
-    db_stub = SimpleNamespace(session=StubSession([tenant, None, end_user]))
 
-    monkeypatch.setattr("core.tools.workflow_as_tool.tool.db", db_stub)
+    # Monkeypatch session factory to return our stub session
+    monkeypatch.setattr(
+        "core.tools.workflow_as_tool.tool.session_factory.create_session",
+        lambda: StubSession([tenant, None, end_user]),
+    )
 
     entity = ToolEntity(
         identity=ToolIdentity(author="test", name="test tool", label=I18nObject(en_US="test tool"), provider="test"),
@@ -266,8 +283,23 @@ def test_resolve_user_from_database_returns_none_when_no_tenant(monkeypatch: pyt
         def scalar(self, _stmt):
             return self.results.pop(0)
 
-    db_stub = SimpleNamespace(session=StubSession([None]))
-    monkeypatch.setattr("core.tools.workflow_as_tool.tool.db", db_stub)
+        def expunge(self, *_args, **_kwargs):
+            pass
+
+        def close(self):
+            pass
+
+        def __enter__(self):
+            return self
+
+        def __exit__(self, exc_type, exc, tb):
+            self.close()
+
+    # Monkeypatch session factory to return our stub session with no tenant
+    monkeypatch.setattr(
+        "core.tools.workflow_as_tool.tool.session_factory.create_session",
+        lambda: StubSession([None]),
+    )
 
     entity = ToolEntity(
         identity=ToolIdentity(author="test", name="test tool", label=I18nObject(en_US="test tool"), provider="test"),