Asp。Net MVC LINQ查询，检查2个日期之间是否已经存在协议

I have an Asp.Net MVC5 project which I need some help with. The Logic is that a Customer needs to have an agreement. This is fine because I can create the first agreement. The problem I am having is that if another agreement needs to be created for the customer it can't be within the same period as the existing one. Initially I am thinking of placing something into the Agreement controller in the Create method to do the check. What I have currently is I have an Asp.Net MVC5 project which I need som