Constant DUPSORT 

pub const DUPSORT: Flags;

Duplicate keys may be used in the database. (Or, from another perspective, keys may have multiple data items, stored in sorted order.) By default keys must be unique and may have only a single data item.

Example

let db = lmdb::Database::open(
  &env, Some("example"), &lmdb::DatabaseOptions::new(
    lmdb::db::DUPSORT | lmdb::db::CREATE)).unwrap();
let txn = lmdb::WriteTransaction::new(&env).unwrap();
{
  let mut access = txn.access();
  let f = lmdb::put::Flags::empty();
  access.put(&db, "Fruit", "Orange", f).unwrap();
  access.put(&db, "Fruit", "Apple", f).unwrap();
  access.put(&db, "Veggie", "Carrot", f).unwrap();

  let mut cursor = txn.cursor(&db).unwrap();
  assert_eq!(("Fruit", "Apple"),
             cursor.seek_k_both(&access, "Fruit").unwrap());
  assert_eq!(("Fruit", "Orange"), cursor.next(&access).unwrap());
  assert_eq!(("Veggie", "Carrot"), cursor.next(&access).unwrap());
}
txn.commit().unwrap();