Automapper first IQueryable.ProjectTo projection is too slow - performance

Question

I have Dto classes:
public class PackageDto
{
public MemberDto Receiver { get; set; }
public MemberDto Sender { get; set; }
public DocflowDto Docflow { get; set; }
public DocflowTypeOption DocflowTypeId { get; set; }
public string Code { get; set; }
public Guid? DocGuid { get; set; }
}
public class LightPackageDto
{
public DocflowDto Docflow { get; set; }
public DocflowTypeOption DocflowTypeId { get; set; }
public string Code { get; set; }
public Guid? DocGuid { get; set; }
}
public class MemberDto
{
public string Prop1 { get; set; }
public EntityTypeOption Prop2 { get; set; }
public string Prop3 { get; set; }
public string Prop4 { get; set; }
public string Prop5 { get; set; }
public PersonDto Director { get; set; }
public string CompanyShortName { get; set; }
public string CompanyFullName { get; set; }
public string CompanyPrefix { get; set; }
}
DocflowDto has 3 simple type properties and is projected by flattening.
PersonDto has 3 simple type properties and is projected by flattening too
Mapping rules:
CreateMap<Person, PersonDto>();
CreateMap<Member, MemberDto>()
.ForMember(dest => dest.Prop1, opt => opt.MapFrom(src => src.Employee.Prop1))
.ForMember(dest => dest.Prop2, opt => opt.MapFrom(src => src.Prop2))
.ForMember(dest => dest.Prop3, opt => opt.MapFrom(src => src.Employee.Prop3))
.ForMember(dest => dest.Prop4, opt => opt.MapFrom(src => src.Employee.Prop4))
.ForMember(dest => dest.Prop5, opt => opt.MapFrom(src => src.Employee.Prop5))
.ForMember(dest => dest.Director, opt => opt.MapFrom(src => src.Employee.Director))
.ForMember(dest => dest.CompanyShortName, opt => opt.MapFrom(src => src.Company.CompanyShortName))
.ForMember(dest => dest.CompanyFullName, opt => opt.MapFrom(src => src.Company.CompanyFullName))
.ForMember(dest => dest.CompanyPrefix, opt => opt.MapFrom(src => src.Company.Prefix))
;
CreateMap<Data.Models.Docflow.Package, PackageDto>()
.ForMember(dest => dest.Sender, opt => opt.MapFrom(src => src.Sender))
.ForMember(dest => dest.Receiver, opt => opt.MapFrom(src => src.Receiver))
.ForMember(dest => dest.Docflow, opt => opt.MapFrom(src => src.Docflow))
.ForMember(dest => dest.DocGuid, opt => opt.MapFrom(src => src.Files.FirstOrDefault().DocGuid))
;
CreateMap<Data.Models.Docflow.Package, LightPackageDto>()
.ForMember(dest => dest.Docflow, opt => opt.MapFrom(src => src.Docflow))
.ForMember(dest => dest.DocGuid, opt => opt.MapFrom(src => src.Files.FirstOrDefault().DocGuid));
Then tests:
//fast
var lightEntity = await _db.Packages.Where(p => p.PackageGuid == packageGuid).ProjectTo<LightPackageDto>().FirstOrDefaultAsync();
//fast (_db.GetPackage make query with all necessary includes)
var entity = await _db.GetPackage(packageGuid);
var entityDto = AutoMapper.Mapper.Map<Package, PackageDto>(entity);
//first run too slow
var result = await _db.Packages.AsNoTracking().Where(p => p.PackageGuid == packageGuid).ProjectTo<PackageDto>().FirstOrDefaultAsync();
1) So if I project to LightPackageDto (without Member projections) is all right.
2) If I return entity manually from EF with includes and then I make mappings for "in memory" entity is all right too
3) If I want Automapper makes "Select" query applying ProjectTo I allways get freeze about 2-3 sec. But freeze appears only single first time. Why?
And additional question. I see in result sql select statement all the columns of all the concerning tables. I supposed to see only columns needed for destination projection. Why are all there?

Answer 1

It is just some stupid bug. It is not caching or anything. Because touching the intended projection and canceling the task is enough to "clean the path" (solution 1). Or (sometimes) converting query to list before getting first element also works (solution 2).
Solution 1:
Works every time for me. (Note that the time (1000 ms in this case) starts counting when CancelAfter method is hit. So debugging step-by-step jumps to catch block almost every time.)
CancellationTokenSource cancelationTokenSource = new CancellationTokenSource();
cancelationTokenSource.CancelAfter(1000);
PackageDto result = null;
try
{
result = await _db.Packages.AsNoTracking()
.Where(p => p.PackageGuid == packageGuid).ProjectTo<PackageDto>()
.FirstOrDefaultAsync(cancelationTokenSource.Token);//cancel this, when taking longer than 1s
}
catch (OperationCanceledException)
{ //do absolutely the same thing, but now it will be fast...
result = await _db.Packages.AsNoTracking()
.Where(p => p.PackageGuid == packageGuid).ProjectTo<PackageDto>()
.FirstOrDefaultAsync();
}
Solution 2:
!!! Doesn't work consistently. Need some more investigation
PackageDto result = await _db.Packages.AsNoTracking()
.Where(p => p.PackageGuid == packageGuid).ProjectTo<PackageDto>()
.ToList().FirstOrDefault();//converting to list for some reason helps here..
Yeah. Not the most beautiful solution, but better than waiting 25 seconds...
(btw .net6, Automapper 10.1.1, AutoMapper.Collection.EntityFrameworkCore 7.1.3)