Remove duplicates from DropDownList from database MVC4

Question

I would like to take data from DB and add it to DropDownList in order to select an item in search panel, I want to remove duplicates items from the list (one author, many books). What should I do?

List<string> authorname = new List<string>();

foreach (var item in DB.Books)
{
    authorname.Add(item.BookDetails.authorname.ToString());
}

ViewData["AuthorName"] = new SelectList(authorname);

Answer 1

Populate the DropDownList with unique values after they have been already selected from the database. Use the 'distinct' keyword in your SQL query in order to achieve this goal.

SELECT DISTINCT column_name,column_name
FROM table_name;

http://www.w3schools.com/sql/sql_distinct.asp

Answer 2

try below

List<string> authorname = new List<string>();

foreach (var item in DB.Books)
{
   if(!authorname.Contains(item.BookDetails.authorname.ToString()))
      authorname.Add(item.BookDetails.authorname.ToString());
}

ViewData["AuthorName"] = new SelectList(authorname);

Answer 3

List<string> authorname = new List<string>();
foreach (string name in DB.Books.Select(x=> new {name = x.authorname}).Distinct())
{
   authorname.Add(name);
}

Answer 4

you can directly use linq and get the distinct items ..

code here

list<string> authorNamesDistinct = (from a in DB.Books
select a.BookDetails.authorname).Distinct().ToList();


ViewData["AuthorName"] = new SelectList(authorNamesDistinct);