The first Map call is very slow

[zraffaele]

Hi,
i've create an ASP NET Core Web API with EF core, this have a lot of relationship within the tables
The automapper is configured with profile: CreateMap<ActivityBase, ActivityBaseModel>().ReverseMap().PreserveReferences();
In the startup register the Mapper register the DI is with services.AddAutoMapper(System.Reflection.Assembly.GetExecutingAssembly());
In the controller first execute the query and the result is mapped with this line of code:
return Mapper.Map(result); The query return one record.
The first time that i execute this line of code is very very slow 10 second, at the second attemp the execution is instant.
Anyone please have any suggestions?
Thanks in advance

RZ

[lbargaoanu]

https://github.com/AutoMapper/AutoMapper/blob/upgrade_guide/docs/Configuration.md#long-compilation-times
Try the MyGet build. Set MaxExecutionPlanDepth to zero. Remove MaxDepth and PreserveReferences.

[lbargaoanu]

@zraffaele Thank you for taking the time to make the repro, apparently there was a bug with MaxExecutionPlanDepth, but as far I can tell, it's solved now.

[Erythnul]

Also potentially a combination effect with EF core model compilation, which can also take quite a bit of time. Unless your mapping is extremely complex this might be a more likely culprit.
FYI, EF core 6 intends to fix this by allowing precompiled models:
https://devblogs.microsoft.com/dotnet/announcing-entity-framework-core-6-0-preview-5-compiled-models/

[zraffaele]

When I call the EF mapping it has already returned the result and loaded all the data into the objects.