Question

i’m using Asp.net MVC with Sharp Architecture.

I have this code:

return _repositoryKeyWord.FindAll(x => x.Category.Id == idCAtegory)
                .Take(50).ToList();

How can i order by random?
Note: i don’t want to order the 50 extracted items, i want order before and then extract 50 items.

thks

Answer 1

One way to achieve efficiently is to add a column to your data Shuffle that is populated with a random int (as each record is created).

The query to access the table then becomes …

Random random = new Random();
int seed = random.Next();
result = result.OrderBy(s => (~(s.Shuffle & seed)) & (s.Shuffle | seed)); // ^ seed);

This does an XOR operation in the database and orders by the results of that XOR.

Advantages:-

1. Efficient: SQL handles the
   ordering, no need to fetch the whole
   table
2. Repeatable: (good for
   testing) – can use the same random
   seed to generate the same random
   order
3. Works on most (all?) Entity Framework supported
   databases

This is the approach used by my home automation system to randomize playlists. It picks a new seed each day giving a consistent order during the day (allowing easy pause / resume capabilities) but a fresh look at each playlist each new day.