Linq to SQL: specified cast is not valid

Question

I want to query to a book in my library database, so I wrote this code...

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Net.Sockets;
using System.Web;

/// <summary>
/// Summary description for Book
/// </summary>
public partial class Book
{
    public static List<Book> GetQueryBooks(string query)
    {
        // Init db
        LibraryDataClassesDataContext db = new LibraryDataClassesDataContext();
        return db.Books.Where(b => b.Title.Contains(query) || b.Author.Contains(query)).ToList();

    } 
}

But I do not get why I get a "InvalidCastException: Specified cast is not valid" on the return?

Answer 1

It looks to me like you are missing a namespace - so Book here (in the class definition) refers to global::Book - rather than whatever-your-LINQ-namespace-is Book . Essentially, then, your partial class Book is a completely different type to the Book that the LibraryDataClassesDataContext knows about.

Try:

namespace The.Correct.Namespace
{
    public partial class Book
    {
        public static List<Book> GetQueryBooks(string query)
        {
            // Init db
            LibraryDataClassesDataContext db = new LibraryDataClassesDataContext();
            return db.Books.Where(b => b.Title.Contains(query) || b.Author.Contains(query)).ToList();

        } 
    }     
}

where The.Correct.Namespace is the namespace that LibraryDataClasses.designer.cs (I'm guessing on the file name here) is using.