Mapper not initialized, When Use ProjectTo()

You need to pass the MappingConfiguration provider to the ProjectTo call.

public async Task<FreelancerProfileViewModel> GetFreelancerProfile()
{
    var id = Guid.Parse(_identity.GetUserId());
    var model = await _freelancerProfiles
        .AsNoTracking()
        .Where(_ => _.User.Id == id)
        .ProjectTo<FreelancerProfileViewModel>(_mapper.Configuration)
        .FirstAsync();

 //  var viewmodel =  _mapper.Map<FreelancerProfileViewModel>(model);

    return model;
}

In the .NET Core 3.1 (AutoMapper 9.0.0) new registration is: services.AddAutoMapper(typeof(Startup));

In the .NET Core 2.1 (AutoMapper 7.0.1) version you have to pass the ConfigurationProvider.

1. Register AutoMapper like described here

2. Inject to the Controller:

   private readonly IMapper _mapper; public SomeController(ApplicationDbContext dbContext, IMapper mapper) { _mapper = mapper; }

3. Pass the ConfigurationProvider this way:

   ApplicationDbContext.SomeEntities.ProjectTo(_mapper.ConfigurationProvider)