ICollection in class

Question

I come across the codes below:

public class Basket
{
    public Guid BasketId { get; set; }
    public DateTime Date { get; set; }

    public virtual ICollection<BasketItem> BasketItems { get; set; }

    public Basket()
    {
        BasketItems = new List<BasketItem>();
    }
}

The part I do not quite understand is that why would we put

public virtual ICollection<BasketItem> BasketItems { get; set; }

instead of

public virtual List<BasketItem> BasketItems { get; set; }

One reason I can think of is that when this class is inherited, we can override BasketItems with different types?

What are other reasons of doing so?

entity framework might be supplying a non-list implementation. — Daniel A. White, May 20 '16 at 01:23

score 3 · Answer 1 · answered May 20 '16 at 01:31

3

Because BasketItems doesn't need to be a list. Notice that the setter is public. It can also be overridden, as you pointed out.

It's essentially saying, as long as BasketItems is a collection of BasketItem, that's all we need to know. We don't care how the collection is implemented.

answered May 20 '16 at 01:31

Rob

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I suspect the public setter is a mistake, or they wouldn't initialize it in the constructor. If you leave a public setter lying around, you need to be prepared to handle `null`s. – Joel Coehoorn May 20 '16 at 01:41

score 3 · Accepted Answer · edited May 23 '17 at 12:23

Avoiding concrete types when possible is normally a good design practice. It actually buys you a lot of strong advantages which are well documented in the Dependency Inversion Principle of SOLID - SOLID Wikipedia. Long story short, not putting yourself into a corner is good design because it allows the user to extend the property as they see fit and it lowers maintenance because, as an author, you don't have to create a new class type for every implementation of ICollection.

Another big benefit here is unit testing. Avoiding concrete types makes it a lot easier to mock dependencies in unit tests. This leads to test being smaller and more precise. There's a good explanation here of the benefits for more info - How do interfaces making unit testing and mocking easier?

score 1 · Answer 3 · answered May 20 '16 at 01:44

1

one more thing: ICollection is usually used in DataEntity for many-many/one-many relationships as well. You can refer (MSDN: http://msdn.microsoft.com/en-us/library/92t2ye13.aspx) is a list of object that needs to be iterated through and modified.

answered May 20 '16 at 01:44

Minh Bui

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ICollection in class

3 Answers3