Custom Value Resolver in Mapster

Question

I've been working with AutoMapper and it was quite joyful but for a number of reasons I got to use Mapster in my new project.

As you may know we had a handy configuration for CustomValueResolvers:

            CreateMap<Context.Models.Employee, EmployeeDTO>()
            .ForMember(dest => dest.CustomValue, opt => opt.MapFrom<EmployeeCustomValueResolver>());

EmployeeCustomValueResolver was a class with its own template you could inject DbContext and read whatever you need and return whatever you want:

 public class EmployeeCustomValueResolver: IValueResolver<Context.Models.Employee, EmployeeDTO, List<anyType>>
{
 //Read whatever you want from db and return.
}

But now in this Mapster I don't know how to do that. I have a type config section like this:

TypeAdapterConfig<Employee, EmployeeDTO>.NewConfig()
            .Map(dest=>dest.Gates,src=>src.Gates.ToList())

but this is not what I want. I want to create a custom class as a custom value resolver and return my Gates as a result and I don't know how? I need something like AutoMapper ValueResolver.

Any help is appreciated.