实体框架将使用的ICollection＆LT; T＆GT; ，因为它需要支持添加的操作，这是不是一部分的的IEnumerable＆LT; T＆GT; 接口

Entity Framework would use ICollection<T> because it needs to support Add operations, which are not part of the IEnumerable<T> interface.

另外请注意，您的是的使用的ICollection＆LT; T＆GT; ，你只是暴露其作为列表＆LT; T＆GT ; 的实施。 列表＆LT; T＆GT; T＆GT; ，的ICollection＆LT; T＆GT; 它的IList＆LT带来沿/ code>和的IEnumerable＆LT; T＆GT;

Also note that you were using ICollection<T>, you were merely exposing it as the List<T> implementation. List<T> brings along with it IList<T>, ICollection<T>, and IEnumerable<T>.

至于你的变化，通过接口暴露是个不错的选择，尽管列表＆LT; T＆GT; 工作。该接口定义了合同，但是没有实现。实施的可能的变化。在某些情况下，也许实现可能是一个的HashSet＆LT; T＆GT; ，例如。 （这是您可以使用的不仅仅是实体框架的更多，顺便一种思维定势，一个良好的面向对象的做法是对的接口，而不是实现编程。实现可以和将发生改变。）

As for your change, exposing via the interface is a good choice, despite List<T> working. The interface defines the contract but not the implementation. The implementation could change. In some instances, perhaps the implementation could be a HashSet<T>, for example. (This is a mindset you could use for more than just Entity Framework, by the way. A good object-oriented practice is to program towards the interface and not the implementation. Implementations can and will change.)