Question

I’ve set up a tagging system

I belive it is the “toxi” solution with the following tables:

Books[id,author, title] has many-to-many relationship with

Tags[id, tagName]

BookHasTag[id, bookId, tagId] junction-table

using linq-sql I want to:

• select the top 20 most popular tags and have their count with it
• given a books id, get all the info about the book, including tags associated with it
• a list of all books that are associated with a particular tag

Please can you help, I know it’s a little cheeky, and I know SO usually like to see you have made an effort, but for the sake of brevity i’m leaving out my failed attempts.

Answer 1

If I understand you correct you want something like this:

select the top 20 most popular tags and have their count with it

var lsTags=(
        from tag in db.Tags
        select new
        {
            tag.id,
            tag.tagName,
            NbrOfTags=
                (
                    from hasTags in db.BookHasTag
                    where hasTags.tagId==tag.id
                    select hasTags.id
                ).Count()
        }
    ).OrderByDescending(a=>a.NbrOfTags).Take(20).ToList();

given a books id, get all the info about the book, including tags associated with it

var bookId=1;
var lsBooksWithTags=(
        from book in db.Books
        where book.id==bookId
        select new
        {
            book.id,
            book.author,
            book.title,
            Tags=(
                    from bookHasTag in db.BookHasTag
                    join tags in db.Tags
                        on bookHasTag.tagId equals tags.id
                    where bookHasTag.bookId==book.id
                    select new
                    {
                        tags.id,
                        tags.tagName
                    }
                )
        }
    ).ToList();

a list of all books that are associated with a particular tag

var tagId=1;
var lsBooksByTagId=(
            from book in db.Books
            where
                (
                    db.BookHasTag.Where(a=>a.tagId==tagId).Select(a=>a.bookId)
                ).Contains(book.id)
            select new
            {
                book.id,
                book.author,
                book.title
            }
        ).ToList();