從應用程式日誌看到下面這個 Entity Framework Core（以下簡稱 EF Core）發出的例外錯誤：
The instance of entity type 'MyTable' cannot be tracked because another instance with the same key value for {'Key'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.
它的意思是，相同主索引鍵的實體無法被追蹤，因為已經有另一個實體正在被追蹤，我們來看看怎麼回事。
