使用ICollection的基本思想是提供一个接口来快速访问有限数量的数据。事实上，你有一个收藏。数属性。IEnumerable更适合于某些数据链，在这些数据链中，你可以读到某个逻辑点，某个消费者特别指定的条件，或者读到枚举的结尾。

使用ICollection<T>是因为IEnumerable<T>接口不提供添加项、删除项或以其他方式修改集合的方法。

我是这样记得的:

IEnumerable has one method GetEnumerator() which allows one to read through the values in a collection but not write to it. Most of the complexity of using the enumerator is taken care of for us by the for each statement in C#. IEnumerable has one property: Current, which returns the current element. ICollection implements IEnumerable and adds few additional properties the most use of which is Count. The generic version of ICollection implements the Add() and Remove() methods. IList implements both IEnumerable and ICollection, and add the integer indexing access to items (which is not usually required, as ordering is done in database).

What I have done in the past is declare my inner class collections using IList<Class>, ICollection<Class>or IEnumerable<Class> (if static list) depending on whether or not I will have to do any number of the following in a method in my repository: enumerate, sort/order or modify. When I just need to enumerate (and maybe sort) over objects then I create a temp List<Class>to work with the collection within an IEnumerable method. I think this practice would only be effective if the collection is relatively small, but it may be good practice in general, idk. Please correct me if there is evidence as to why this would not good practice.

导航属性通常被定义为虚拟的，这样它们就可以利用某些实体框架的功能，比如延迟加载。

如果一个导航属性可以保存多个实体(如在多对多或一对多关系中)，那么它的类型必须是一个列表，其中可以添加、删除和更新条目，例如ICollection。

https://www.asp.net/mvc/overview/getting-started/getting-started-with-ef-using-mvc/creating-an-entity-framework-data-model-for-an-asp-net-mvc-application

回复你关于List<T>的问题:

List<T>是一个类;指定接口可以使实现更加灵活。一个更好的问题是“为什么不IList<T>?”

要回答这个问题，请考虑IList<T>向ICollection<T>:整数索引添加了什么，这意味着项具有某种任意顺序，并且可以通过引用该顺序来检索。这在大多数情况下可能没有意义，因为项目可能需要在不同的上下文中以不同的顺序排列。