fix(api): fix DetachedInstanceError for Account.current_tenant_id (langgenius#24789)

The `Account._current_tenant` object is loaded by a database session (typically `db.session`) whose lifetime 
is not aligned with the Account model instance. This misalignment causes a `DetachedInstanceError` to be raised
when accessing attributes of `Account._current_tenant` after the original session has been closed.

To resolve this issue, we now reload the tenant object with `expire_on_commit=False`, ensuring the tenant remains
accessible even after the session is closed.

Author: QuantumGhost

api/models/account.py

@@ -1,12 +1,12 @@
 import enum
 import json
 from datetime import datetime
-from typing import Optional, cast
+from typing import Optional
 
 import sqlalchemy as sa
 from flask_login import UserMixin
 from sqlalchemy import DateTime, String, func, select
-from sqlalchemy.orm import Mapped, mapped_column, reconstructor
+from sqlalchemy.orm import Mapped, Session, mapped_column, reconstructor
 
 from models.base import Base
 
@@ -118,10 +118,24 @@ def current_tenant(self):
 
     @current_tenant.setter
     def current_tenant(self, tenant: "Tenant"):
-        ta = db.session.scalar(select(TenantAccountJoin).filter_by(tenant_id=tenant.id, account_id=self.id).limit(1))
-        if ta:
-            self.role = TenantAccountRole(ta.role)
-            self._current_tenant = tenant
+        with Session(db.engine, expire_on_commit=False) as session:
+            tenant_join_query = select(TenantAccountJoin).where(
+                TenantAccountJoin.tenant_id == tenant.id, TenantAccountJoin.account_id == self.id
+            )
+            tenant_join = session.scalar(tenant_join_query)
+            tenant_query = select(Tenant).where(Tenant.id == tenant.id)
+            # TODO: A workaround to reload the tenant with `expire_on_commit=False`, allowing
+            # access to it after the session has been closed.
+            # This prevents `DetachedInstanceError` when accessing the tenant outside
+            # the session's lifecycle.
+            # (The `tenant` argument is typically loaded by `db.session` without the
+            # `expire_on_commit=False` flag, meaning its lifetime is tied to the web
+            # request's lifecycle.)
+            tenant_reloaded = session.scalars(tenant_query).one()
+
+        if tenant_join:
+            self.role = TenantAccountRole(tenant_join.role)
+            self._current_tenant = tenant_reloaded
             return
         self._current_tenant = None
 
@@ -130,23 +144,19 @@ def current_tenant_id(self) -> str | None:
         return self._current_tenant.id if self._current_tenant else None
 
     def set_tenant_id(self, tenant_id: str):
-        tenant_account_join = cast(
-            tuple[Tenant, TenantAccountJoin],
-            (
-                db.session.query(Tenant, TenantAccountJoin)
-                .where(Tenant.id == tenant_id)
-                .where(TenantAccountJoin.tenant_id == Tenant.id)
-                .where(TenantAccountJoin.account_id == self.id)
-                .one_or_none()
-            ),
+        query = (
+            select(Tenant, TenantAccountJoin)
+            .where(Tenant.id == tenant_id)
+            .where(TenantAccountJoin.tenant_id == Tenant.id)
+            .where(TenantAccountJoin.account_id == self.id)
         )
-
-        if not tenant_account_join:
-            return
-
-        tenant, join = tenant_account_join
-        self.role = TenantAccountRole(join.role)
-        self._current_tenant = tenant
+        with Session(db.engine, expire_on_commit=False) as session:
+            tenant_account_join = session.execute(query).first()
+            if not tenant_account_join:
+                return
+            tenant, join = tenant_account_join
+            self.role = TenantAccountRole(join.role)
+            self._current_tenant = tenant
 
     @property
     def current_role(self):