How to flatten nested objects with linq expression

Question

I am trying to flatten nested objects like this:

public class Book
{
    public string Name { get; set; }
    public IList<Chapter> Chapters { get; set; }
}

public class Chapter
{
    public string Name { get; set; }
    public IList<Page> Pages { get; set; }
}


public class Page
{
    public string Name { get; set; }
}

Let me make an example. This is the data I have

Book: Pro Linq 
{ 
   Chapter 1: Hello Linq 
   {
      Page 1, 
      Page 2, 
      Page 3
   },
   Chapter 2: C# Language enhancements
   {
      Page 4
   },
}

The result I am looking for is the following flat list:

"Pro Linq", "Hello Linq", "Page 1"
"Pro Linq", "Hello Linq", "Page 2"
"Pro Linq", "Hello Linq", "Page 3"
"Pro Linq", "C# Language enhancements", "Page 4"

How could I accomplish this? I could do it with a select new but I've been told that a SelectMany would be enough.

Solution 1

myBooks.SelectMany(b => b.Chapters
    .SelectMany(c => c.Pages
        .Select(p => b.Name + ", " + c.Name + ", " + p.Name)));

Solution 2

Assuming books is a List of Book:

var r = from b in books
    from c in b.Chapters
    from p in c.Pages
    select new {BookName = b.Name, ChapterName = c.Name, PageName = p.Name};

Solution 3

myBooks.SelectMany(b => b.Chapters
    .SelectMany(c => c.Pages
        .Select(p => new 
                {
                    BookName = b.Name ,
                    ChapterName = c.Name , 
                    PageName = p.Name
                });

Comments

[Sam]

+1, even though any IEnumerable<Book> will do, doesn't need a List<Book>.

[ab_732]

Awesome!!! What if I would have a result a new object, like FlatBook{BookName, ChapterName, PageName} ?

[Sam]

@abx78: simply alter the last select: .Select(p => new FlatBook(b.Name, c.Name, p.Name))

[ab_732]

Thank you guys, this was what I need!

[Homer]

does this produce the same result? myBooks.SelectMany(b => b.Chapters).SelectMany(c => c.Pages).Select(p => b.Name + ", " + c.Name + ", " + p.Name);

[The Muffin Man]

So how would you rewrite this to support an N number of nested objects?

[Mastro]

Is there a way to do this but include any Books that do not have Chapters?

[Yuriy Faktorovich]

@Mastro start it with myBooks.Where(b => b.Chapters != null)

[Mastro]

Hmm well I wanted a list where both are shown. what you have here is where not null, I wanted a flatten list where I also, include the nulls but doesn't seem to work if I do Where(b => b.Chapters == null) as I get 0. Would like to have a flatten list with all books, ones with or without chapters. Is that possible? Or do I need some type of union?

[Yuriy Faktorovich]

@Mastro how about myBooks.SelectMany(b => b.Chapters == null || !b.Chapters.Any()? new []{b.Name + " has no Chapters"} : b.SelectMany(c => c.Pages.Select(p => b.Name + ", " + c.Name + ", " + p.Name)));

[Mastro]

Ok that code didn't help but it got my on my track to solving it. So gonna vote up your comment for the effort.

[Yuriy Faktorovich]

@Mastro did I misunderstand what you were asking? What was the solution?

[Mastro]

Well I couldn't get yours to compile but I don't have books to chapters, I have projects(b) to companyperson(c) to companies(p). So I used linqPad and created a left join query. Too long to post here it seems, I'll post as an answer.

[oɔɯǝɹ]

While this code sample may answer the question, it lacks explanation. As it stands now, it adds no value, and stands the change of being downvoted / deleted. Please add some explanation what is does and why it is a solution for the problem of the OP.

[Dejavu]

@Homer: I don't think your solution is possible, since b and c are inaccessible from the last Select clause. See live demo: rextester.com/BHNH3184

[Homer]

@Dejavu, yeah my comment stinks. I'm not even sure what the point of it was.

[mko]

@YuriyFaktorovich but book.name is missing. this code only joins data from chapters and its childs

[Pouya BCD]

Succinct! Thanks.