Question

I’m interested on solution how to use Futures in counting something having Linq in mind. I’m not interested in Criteria api, just plain linq.

If I have:

IEnumerable<User> dbUsers = userquery.Future<User>(); 
IFutureValue<long> count = totalcountQuery.FutureValue<long>(); 

direct translation should be:

var dbUsers = userQuery.ToFuture();     
var count = userQuery.LongCount(); 

Now I need to access count query to know exact number of populated records;

something like this, although this code wont compile:

totalRecords = (int)count.Value;

Answer 1

This is not directly supported by NHibernate, but it is very easy to implement (explained in this blog post). You need to write a new extension method.

public static IFutureValue<TResult> ToFutureValue<TSource, TResult>
    (this IQueryable<TSource> source, Expression<Func<IQueryable<TSource>, TResult>> selector)
    where TResult:struct  where TSource: class
{
    var provider = (INhQueryProvider) source.Provider;
    var method = ((MethodCallExpression) selector.Body).Method;
    var expression = Expression.Call(null, method, source.Expression);
    return (IFutureValue<TResult>) provider.ExecuteFuture(expression);
}

Then it is easy to get a paged query

var query = session.Query<User>().Where(...);
var count = query.ToFutureValue(u => u.Count());
var results = query.OrderBy(u => u.FullName).Skip(n).Take(m).ToFuture()