Question: I am using AUtomapper which I am very impressed with however, I have a complex object with many nested collections. I'm using Telerik OpenAccess and it returns the 1400 records fast but when I pass it to Automapper and it slows to a ridiculous crawl. Here is my code for reference:

```
        List<DAL.Event> query = httpContext.Events.Where(e => e.Inactive != true && e.Event_Locations != null).ToList();
        Mapper.CreateMap<DAL.Event, EventDTO>();
        Mapper.CreateMap<DAL.Event_Association, EventAssociationDTO>();
        Mapper.CreateMap<DAL.Event_ExecutingUnit, EventExecutingUnitDTO>();
        Mapper.CreateMap<DAL.Event_Funding, EventFundingDTO>();
        Mapper.CreateMap<DAL.Event_Location, EventLocationDTO>();
        Mapper.CreateMap<DAL.Event_Objective, EventObjectiveDTO>();
        Mapper.CreateMap<DAL.Event_OSR, EventOSRDTO>();
        Mapper.CreateMap<DAL.Event_PaxBreakDown, EventPAXBreakDownDTO>();
        Mapper.CreateMap<DAL.Event_RegionalConsideration, EventRegionalConsiderationDTO>();
        Mapper.CreateMap<DAL.Event_ReviewStatus, EventReviewStatusDTO>();
        Mapper.CreateMap<DAL.Event_SPCalendarClone, EventSPCalendarClonesDTO>();
        Mapper.CreateMap<DAL.Event_Task, EventTasksDTO>();
        Mapper.CreateMap<DAL.Event_TSO, EventTSOsDTO>();
        Mapper.AssertConfigurationIsValid();
        Mapper.AllowNullDestinationValues = true;

        IList<EventDTO> result = Mapper.Map<List<DAL.Event>, List<EventDTO>>(query);
        return result;

```

HELP!

Answer: 
There was a team at my previous job who were also using Automapper but in the end they removed it because of the performance impact.

I think in this specific scenario it's best to write the mapping code yourself, or start replacing them one by one. Maybe one mapping is causing the bad performance?
For those coming to this later, AutoMapper 5.x release made significant performance improvements, where mapping speed is only slightly slower than hand mapping (1M items):

* Native: 0.19s
* AutoMapper: 0.49s
* AutoMapper 4.2.1: 29s