如何避免EF中新添加的记录的乐观并发错误

I use Entity Framework 6 in an MVC 5 project an there is an entity relations between Experiment and FileAttachment (one Experiment can gave many FileAttachment). During Edit an Experiment record, I load a ViewModel containing both of the entities and list the attachments under the experiment in edit mode: I use Entity Framework 6 in an MVC 5 project an