Question

I want to add the where clause to a linq statement, but it doesn’t behave as i would expected it to.
When i use this code:

IQueryable<Employee> EmpQuery = from e in Session.Query<Employee>() where e.Surname == "Test" select e;
        EmpQuery.ToList();

or i use this code:

IQueryable<Employee> EmpQuery = (from e in Session.Query<Employee>() select e).Where(e => e.Surname == "Test");
        EmpQuery.ToList();

The where clause is included in the SQL command, but when i try it this way:

IQueryable<Employee> EmpQuery = from e in Session.Query<Employee>() select e;
        EmpQuery.Where(e => e.Surname == "Test");

The where clause is not included in the SQL command. Why is this? Is there another way to dynamically add criteria to a Nhibernate Linq query?

Answer 1

You’re not using the return value of Where. LINQ is designed around functional concepts – calling Where doesn’t modify the existing query, it returns a new query which applies the filter. The existing query remains as it was – which means you can reuse it for (say) a different filter.

Note that your current query expression (from x in y select x, effectively) is pretty pointless. I would suggest simply writing:

var query = Session.Query<Employee>().Where(e => e.Surname == "Test");