StackOverflow2013

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copied!<p>On the first part, the interesting restriction is that the book has to match every tag entered, so a where clause of "where tagid == someId" wouldn't really work. I envision something like this (LINQ-to-objects example)</p> <pre><code>List<int> selectedTagIds = new List<int>() { 1, 2 }; var query = from book in books join booktag in booktags on book.Id equals booktag.BookId join selectedId in selectedTagIds on booktag.TagId equals selectedId group book by book into bookgroup where bookgroup.Count() == selectedTagIds.Count select bookgroup.Key; </code></pre> <p>Which basically performs a join from books to booktags and also to the list of selected tag ids and restricts the selection to where the count of book->tag matches equals the count of selected tag ids. </p> <p>To pull the related tags, maybe something like this </p> <pre><code>var relatedTags = from book in query // use original query as base join booktag in booktags on book.Id equals booktag.BookId join tag in tags on booktag.TagId equals tag.Id where !selectedTagIds.Contains(tag.Id) // exclude selected tags from related tags group tag by tag into taggroup select new { Tag = taggroup.Key, Count = taggroup.Count() }; </code></pre> <p>Full code for the quick example. Not fully OOP, but you get the idea.</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; namespace StackOverflow { class Program { static void Main() { List<Book> books = new List<Book>() { new Book() { Id = 113421, Title = "A" }, new Book() { Id = 113422, Title = "B" } }; List<Tag> tags = new List<Tag>() { new Tag() { Id = 1, Name = "ASP" }, new Tag() { Id = 2, Name = "C#" }, new Tag() { Id = 3, Name = "CSS" }, new Tag() { Id = 4, Name = "VB" }, new Tag() { Id = 5, Name = "VB.NET" }, new Tag() { Id = 6, Name = "PHP" }, new Tag() { Id = 7, Name = "Java" }, new Tag() { Id = 8, Name = "Pascal" } }; List<BookTag> booktags = new List<BookTag>() { new BookTag() { Id = 1, BookId = 113421, TagId = 1 }, new BookTag() { Id = 2, BookId = 113421, TagId = 2 }, new BookTag() { Id = 3, BookId = 113421, TagId = 3 }, new BookTag() { Id = 4, BookId = 113421, TagId = 4 }, new BookTag() { Id = 5, BookId = 113422, TagId = 1 }, new BookTag() { Id = 6, BookId = 113422, TagId = 4 }, new BookTag() { Id = 7, BookId = 113422, TagId = 8 } }; List<int> selectedTagIds = new List<int>() { 1,2 }; // get applicable books based on selected tags var query = from book in books join booktag in booktags on book.Id equals booktag.BookId join selectedId in selectedTagIds on booktag.TagId equals selectedId group book by book into bookgroup where bookgroup.Count() == selectedTagIds.Count select bookgroup.Key; foreach (Book book in query) { Console.WriteLine("{0}\t{1}", book.Id, book.Title); } // get related tags for selected tags var relatedTags = from book in query // use original query as base join booktag in booktags on book.Id equals booktag.BookId join tag in tags on booktag.TagId equals tag.Id where !selectedTagIds.Contains(tag.Id) // exclude selected tags from related tags group tag by tag into taggroup select new { Tag = taggroup.Key, Count = taggroup.Count() }; foreach (var relatedTag in relatedTags) { Console.WriteLine("{0}\t{1}\t{2}", relatedTag.Tag.Id, relatedTag.Tag.Name, relatedTag.Count); } Console.Read(); } } class Book { public int Id { get; set; } public string Title { get; set; } } class Tag { public int Id { get; set; } public string Name { get; set; } } class BookTag { public int Id { get; set; } public int BookId { get; set; } public int TagId { get; set; } } } </code></pre> <p>So for selected tags 1 & 2, you'll get book A, and the related tags would be 3 (CSS) and 4 (VB).</p>

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