CODEWITHSUNDEEP
c#linq
Paul
Paul

Reputation: 23

Dynamic Linq - How to select parent objects from child properties

In my example, I have Libraries and Books.. I need to return libraries that have a certain book. I can do this fine using standard LINQ Where(.Any()), but having difficulty using Dynamic Linq.

Below is example code. My error occurs on object l4. 

protected void Page_Load(object sender, EventArgs e)
    {
        List<Library> libraries = new List<Library>();
        libraries.Add( new Library() { Name = "New York" }); // NO BOOKS FOR NY

        List<Book> books = new List<Book>();
        books.Add(new Book() { Title = "Colors" });
        books.Add(new Book() { Title = "Gardening for Noobs" });
        libraries.Add(new Library() {Name = "Boston", Books = books });

        // GET NEW YORK LIBRARY
        List<Library> l1 = libraries.Where(x => x.Name == "New York").ToList();  // STANDARD
        List<Library> l2 = libraries.AsQueryable().Where("Name = \"New York\"").ToList();  // DLINQ

        // GET LIBRARIES WITH BOOK = COLORS
        List<Library> l3 = libraries.Where(x => x.Books != null && x.Books.Any(a => a.Title == "Colors")).ToList(); // STANDARD
        List<Library> l4 = libraries.AsQueryable().Where("Books.any(Title = \"Colors\"").ToList(); // ERROR: No property or field 'Title' exists in type 'Library'

    }


    public class Library
    {
        private string _name;
        private List<Book> _books;
        public string Name
        {
            get { return _name; }
            set { _name = value; }
        }
        public List<Book> Books
        {
            get { return _books; }
            set { _books = value; }
        }
    }

    public class Book
    {
        private string _title;
        public string Title
        {
            get { return _title; }
            set { _title = value; }
        }
    }

Upvotes: 0

Views: 813

Answers (2)

Ilya Sulimanov
Ilya Sulimanov

Reputation: 7856

You missed one bracket and null cheking. Now it works fine

   List<Library> l4 = libraries.AsQueryable().Where("Books != null && Books.any(Title = \"Colors\")").ToList();

Update: I think that problem not in this part your code: https://dotnetfiddle.net/F2uTie

Upvotes: 1

Michael Coxon
Michael Coxon

Reputation: 5520

From memory you need to Select Books before you can use it. This only applies to navigation properties like Books...

List<Library> l4 = libraries.AsQueryable()
    .SelectMany("Books")
    .Where("Title = \"Colors\"")
    .Select("Library")
    .ToList();

You are going to need to add Library to Book

Upvotes: 0

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