ASP.NET Entity Framework 6 HashSet or List for a collection?

Question

My EF models look like this:

public class ContentStatus
{
    public ContentStatus()
    {
        this.Contents = new List<Content>();
    }

    public int ContentStatusId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Content> Contents { get; set; }
}

However I have also seen implementatins looking like this:

public class ContentStatus
{
    public ContentStatus()
    {
        this.Contents = new HashSet<Content>();
    }

    public int ContentStatusId { get; set; }
    public string Name { get; set; }
    public virtual ICollection<Content> Contents { get; set; }
}

Here is the DDL for this Object:

CREATE TABLE [dbo].[ContentStatus] (
    [ContentStatusId] INT           NOT NULL,
    [Name]            NVARCHAR (50) NOT NULL,
    CONSTRAINT [PK_ContentStatus] PRIMARY KEY CLUSTERED ([ContentStatusId] ASC)
);

Can anyone tell me which I should use or even is there a difference and when would I use the List and when the HashSet if that applies.

Thanks

Answer 1

It depends on your use case but in most cases you can add an item to the collection only once because for example each status is applied only once to a content. I doubt you can have one content appear twice in a status. Therefore HashSet is the correct data structure as it will prevent duplicates. In case where one item can be duplicated List would be correct but I have not encountered this in practice and do not even know how EF would handle it.

As a side note I would advise that you do not include a collection of items in your entities unless you need it. For example if you are building a web app to list products you probably have a view where you display a single product together with its tags. Therefore Product should have a collection of Tags to make this case easy. However you probably do not have a page that displays a Tag with its collection of products and therefore the Tag should not have a Products property. It just doesn't care about related products. It seems that this Status entity does not care about its collection of Contents.