How to Rank your search results with multiple search terms using LINQ and EntityFramework

I have always used a ranked search criteria, it's the only true way to get good results back from a data set.  But I've been doing my ranking within C# code.  But this got all the data from the data source and then ranked the results.  This is very poor on performance, as we should only be returning back the results for the page size we require.

So task at hand it to produce a LINQ statement to reterive only the data you require.

Here is the solution:

var entity = new myEntities();

var searchTerm = "a b Ba";

var searchArray = searchTerm.Split(new[] { ' ' }, StringSplitOptions.RemoveEmptyEntries);

var usersAll = entity.User.AsExpandable().Where(TC_User.ContainsInLastName(searchArray));

Console.WriteLine("Total Records: {0}", usersAll.Count());

var users = usersAll
    .Select(x => new { 
        x.LastName, 
        Rank = searchArray.Sum(s => ((x.LastName.Length - x.LastName.Replace(s, "").Length) / s.Length)) });

var results = users.OrderByDescending(o => o.Rank)
    .Skip(0)
    .Take(20);

foreach (var user in results)
{
    Console.WriteLine("{0}, {1}", user.LastName, user.Rank);
}

Console.ReadLine();

You'll also need to add a new method to your User class to check for that the search term is contain in the LastName

public static Expression<Func<TC_User, bool>> ContainsInLastName(
                                                params string[] keywords)
{
    var predicate = PredicateBuilder.False<TC_User>();
    foreach (string keyword in keywords)
    {
        string temp = keyword;
        predicate = predicate.Or(p => p.LastName.Contains(temp));
    }
    return predicate;
}

One thing that is required is LinqKit, which is available via NuGet to handle the PredicateBuilder and AsExpandable.

Watch out as the results coming back from Sum is a BigInt so if you create a model to return back make sure it is a long type.