Yield Return Over Child Objects

Question

I have a list of items ('sections') which has a getter and a setter. Each one of these 'sections' has a list of 'items'. I'd like to provide a yield return property to expose an 'Items' property as an IEnumerable on the containing class. I just can't get the syntax quite right. Do I need another loop in here or will that iterate too many times?

    public virtual IList<ISection> Sections{ get; set; }

    public virtual IEnumerable<IItem> Sections {
        get{
            foreach (var sect in Sections) {
                // will this iterate too many times if I add an additional loop?
                yield return sect.Items
            }
        }
    }

You have a name collision as well. I would recommend renaming the second method to `public virtual IEnumerable SectionItems` since that's what it's returning anyway. — D Stanley, Mar 23 '12 at 13:18

score 6 · Answer 1 · answered Mar 23 '12 at 13:13

You are correct; the extra loop should do what you want - although you won't then know from the calling code which section the item belonged to. So if that's a requirement you may want to rethink your code.

public virtual IEnumerable<IItem> Sections {
    get{
        foreach (var sect in Sections) {
            foreach (var item in sect.Items) {
                yield return item;
            }
        }
    }

score 3 · Accepted Answer · answered Mar 23 '12 at 13:16

3

You could also use SelectMany

public virtual IEnumerable<IItem> Sections 
{
    get { return Sections.SelectMany(s => s.Items); }
}

answered Mar 23 '12 at 13:16

Mike Two

44,935
9
80
96

1

I love an excuse to use a Linq extension. – Echilon Mar 23 '12 at 13:19
You can get more information about `SelectMany` here http://stackoverflow.com/q/958949/23659 – Mike Two Mar 23 '12 at 14:01

score 1 · Answer 3 · answered Mar 23 '12 at 13:20

As mentioned, you can't have two properties with the same name that return different types. You need to rename one of the methods.

Also, you can make the property a one-liner with Linq:

    public virtual IList<ISection> Sections { get; set; }

    public virtual IEnumerable<IItem> SectionItems
    {
        get {
            return Sections.SelectMany(sect => sect.Items);
        }
    }

Yield Return Over Child Objects

3 Answers3