Temporal Relationship Tr:Tx

This is an example of an index with a Tr:Tx relationship. All revisions of employees are indexed by their name and their hiring manager's name on the day they were hired. Complexity arises when its possible that employee had no hiring manager.

public class Employees_ByHiringManager : AbstractIndexCreationTask<Employee, EmployeeWithManager>
{
    public Employees_ByHiringManager()
    {
        Map = employees => 
        
        from employee in employees

        // filter the index to just revisions
        let status = MetadataFor(employee).Value<TemporalStatus>(TemporalMetadata.RavenDocumentTemporalStatus)
        where status == TemporalStatus.Revision
        
        // employee.Id will refer to the full revision key "employees/1/temporalrevisions/2"
        // so we need to truncate it to get back the true employeeId
        let employeeId = employee.Id.Substring(0, employee.Id.Length - TemporalConstants.TemporalKeySeparator.Length - 1)
        
        // Find the revision of the employee that was effective on the hire date.
        // Note that we have to use the history document for this.
        // Revision 1 isn't necessarily the correct revision, because it may have been artifacted.
        let employeeRevAtHiring = LoadDocument<Employee>(
           LoadDocument<TemporalHistory>(employeeId + TemporalHistory.KeyExt)
               .Revisions.First(x => x.Status == TemporalStatus.Revision &&
                                     x.EffectiveStart <= employee.HireDate &&
                                     x.EffectiveUntil > employee.HireDate).Key)
        
        // If the employee has a manager, find the revision of that manager that was effective on the hire date.
        // The null check is important, because it is possible there was no manager on the hire date.
        let manager = employeeRevAtHiring.ManagerId == null
                         ? null
                         : LoadDocument<Employee>(
                             LoadDocument<TemporalHistory>(employeeRevAtHiring.ManagerId + TemporalHistory.KeyExt)
                                 .Revisions.First(x => x.Status == TemporalStatus.Revision &&
                                                       x.EffectiveStart <= employee.HireDate &&
                                                       x.EffectiveUntil > employee.HireDate).Key)
        
        // We should now have the items to index.  Don't forget to handle the null manager.
        select new
        {
           employee.Name,
           Manager = manager == null ? null : manager.Name
        };

        // The manager field is stored so we can return it in a projection.
        Store(x => x.Manager, FieldStorage.Yes);
    }
}