Question

Is it possible to refactor following query so i.Title.Contains(query) || i.Description.Contains(query) is there only once while staying within single query (no subqueries) in the resulting sql?

if (extendedSearch)
{
    result = result.Where(i => i.Title.Contains(query) || i.Description.Contains(query)
        || (i.CreatedBy.FirstName + " " + i.CreatedBy.LastName).Contains(query)
        || (i.AssignedTo.FirstName + " " + i.AssignedTo.LastName).Contains(query)
    );
}
else
    result = result.Where(i => i.Title.Contains(query) || i.Description.Contains(query));

Answer 1

result = result.Where(i => 
    i.Title.Contains(query) || i.Description.Contains(query)
 || (extendedSearch && 
      ((i.CreatedBy.FirstName + " " + i.CreatedBy.LastName).Contains(query)
   ||  (i.AssignedTo.FirstName + " " + i.AssignedTo.LastName).Contains(query))));

(keeping fingers crossed that brackets are correct…)

Logical structure in Where expression: A or (extendedSearch and B)

If extendedSearch is false the result depends only on A. If extendedSearch is true the result depends on (A or B) – which represents the logic in your query, I hope.