ASP中缺少外键关系。NET MVC应用程序使用代码优先的方法与实体框架

I am building an ASP.NET MVC 5 "To Do List" app, where users can add categories and add tasks to categories. I am using Entity Framework 7 with a sort of "Code First" approach, but using an existing database.I am building an ASP.NET MVC 5 "To Do List" app