What Indexes Are

In the below example we create an index that maps documents from the Employees collection and enables querying by FirstName, LastName, or both.

• First, we need to create an index.
  One way to create it is to use the AbstractIndexCreationTask, but there are other ways available as well (you can read about them here).
  

  public class Employees_ByFirstAndLastName : AbstractIndexCreationTask<Employee>
  {
      public Employees_ByFirstAndLastName()
      {
          Map = employees => from employee in employees
                             select new
                             {
                                 FirstName = employee.FirstName,
                                 LastName = employee.LastName
                             };
      }
  }

• The next step is to send an index to a server (more about index deployment options can be found here) so the indexing process can start indexing documents.
  

  // save index on server
  new Employees_ByFirstAndLastName().Execute(store);

• Now, our index can be queried and indexed results can be returned.
  

  IList<Employee> results = session
      .Query<Employee, Employees_ByFirstAndLastName>()
      .Where(x => x.FirstName == "Robert")
      .ToList();