fix(admin): allow clearing data limit with null

app/db/crud/admin.py

@@ -190,8 +190,12 @@ async def update_admin(db: AsyncSession, db_admin: Admin, modified_admin: AdminM
     if modified_admin.status is not None and modified_admin.status != db_admin.status:
         db_admin.status = modified_admin.status
         db_admin.last_status_change = datetime.now(UTC)
-    if modified_admin.data_limit is not None:
-        db_admin.data_limit = modified_admin.data_limit if modified_admin.data_limit > 0 else None
+    if "data_limit" in modified_admin.model_fields_set:
+        db_admin.data_limit = (
+            modified_admin.data_limit
+            if modified_admin.data_limit is not None and modified_admin.data_limit > 0
+            else None
+        )
         # Recompute limited/active based on new data_limit — never touch disabled
         if db_admin.status != AdminStatus.disabled:
             should_be_limited = (

tests/api/test_admin.py

@@ -1358,6 +1358,37 @@ def test_admin_data_limit_zero_means_unlimited(access_token):
         delete_admin(access_token, admin["username"])
 
 
+def test_admin_data_limit_null_means_unlimited(access_token):
+    """Explicit data_limit=null clears the limit while an omitted field leaves it unchanged."""
+    admin = create_admin(access_token)
+    try:
+        response = client.put(
+            f"/api/admin/{admin['username']}",
+            json={"data_limit": 1073741824},
+            headers=auth_headers(access_token),
+        )
+        assert response.status_code == status.HTTP_200_OK
+        assert response.json()["data_limit"] == 1073741824
+
+        response = client.put(
+            f"/api/admin/{admin['username']}",
+            json={"note": "keep the existing limit"},
+            headers=auth_headers(access_token),
+        )
+        assert response.status_code == status.HTTP_200_OK
+        assert response.json()["data_limit"] == 1073741824
+
+        response = client.put(
+            f"/api/admin/{admin['username']}",
+            json={"data_limit": None},
+            headers=auth_headers(access_token),
+        )
+        assert response.status_code == status.HTTP_200_OK
+        assert response.json()["data_limit"] is None
+    finally:
+        delete_admin(access_token, admin["username"])
+
+
 def test_admin_status_defaults_to_active(access_token):
     """Newly created admin has status=active."""
     admin = create_admin(access_token)