Instance creation of derived class from an abstract class

[jigneshkvp]

Hello @eswann , @chaowlert,

I am facing a particular issue where I have a derived class inheriting from a base abstract class and Mapster give me an error "Instances of abstract classes cannot be created". Consider the example below:

I have a TPT database model, where my Car inherits from Vehicle, my EF model reflects it.

My Dto objects are:

public class ProductDto
{
  public List<VehicleDto> Vehicles { get; set; }
}

[KnownType(typeof(CarDto)]
public abstract class VehicleDto
{
  public int Id { get; set; }
  public string Name { get; set; }
}

public class CarDto : VehicleDto
{
  public string Make { get; set; }
  public string ChassiNumber { get; set; }
}

My Mapping is:

TypeAdapterConfig<Product, ProductDto>.NewConfig(); //Product is a table in db
TypeAdapterConfig<Vehicle, VehicleDto>.NewConfig(); // Vehicle is a table in the db
TypeAdapterConfig<Car, CarDto> // Car is a table in the db
      .NewConfig()
      .Inherits<Vehicle, VehicleDto>;

The actual call

 var product = context.GetProductById(1); // returns the list of Vehicle - containing type Car 
 var productDto = product.Adapt<ProductDto>(); // Exception is throw here. Where I expect my list  of VehicleDto will be mapped (as list of type CarDto)

What wrong am I doing? Is there any mapping registration issue? or Mapster is unable to handle abstract class? Please let me know.

Thanks!

[BuzzDee3000]

Hi jigneshkvp,
have you tried to define a custom constructor configuration?

//Example using a non-default constructor TypeAdapterConfig<TSource, TDestination>.NewConfig() .ConstructUsing(src => new TDestination(src.Id, src.Name));

[eswann]

THanks for the heads-up, the abstract type should be ok. I'll add a test case to test this in a bit.

[eswann]

Ahh...I see the issue now. Because your ProductDto has a list of VehicleDto, it's trying to map to the VehicleDto type (meaning it will try to new up this type). It can't assume you want to map to CarDto just because that is one mapping that is defined. You have to know the destination type you are mapping to. Problem is that if you have several vehicle types, you'll need some kind of logic in the mapping to differentiate the type to map to.

[chaowlert]

This is interesting issue. I will check how EF can return information from abstract class. For now, could you remove from abstract modifier from VehicleDto class?

[jigneshkvp]

Hi,

I managed to do something like this as suggested by BuzzDee3000 (Thanks!):

TypeAdapterConfig<Vehicle, VehicleDto>.NewConfig()
.ConstructUsing(src => MapVehicle(src));

public VehicleDto MapVehicle(Vehicle vehicle)
{
  var vehicleType = vehicle.GetType().BaseType;
  if(vehicleType == null) return null;

  if(vehicleType.FullName == typeOf(Car).Name)
      return new CarDto();

 if(vehicleType.FullName == typeOf(Truck).Name)
      return new TruckDto();  

 return null;
}

In AutoMapper 4.2.1, inheritance is handled as follows and it automatically takes care of instantiating concrete classes from abstract classes:

var config = new MapperConfiguration(cfg =>  
                           {
                                  cfg.CreateMap<Vehicle, VehicleDto>()
                                       .Include<Car, CarDto>()
                                       .Include<Truck, TruckDto>();
                           });

It would have been really great if we could have something similar in Mapster.

Also, what I do use in AutoMapper is the "Profile" class, which provides named configuration for maps.

using AutoMapper;
public class VehicleProfile : Profile
{
   protected override void Configure()
    {
         var config = new MapperConfiguration(cfg =>  
                           {
                                  cfg.CreateMap<Vehicle, VehicleDto>()
                                       .Include<Car, CarDto>()
                                       .Include<Truck, TruckDto>();
                           });
    }
}

So I can register/add all profiles during Application_Start and then my Mapping is done once for the session. I then resolve the mapping using the "MappingEngine" class which I pass as a dependency wherever required.

Could you suggest me something similar in Mapster?

Thanks for your quick response! 👍

[eswann]

Hi @jigneshkvp , it make sense to see if we have a mapping that qualifies as a "default/defined" mapping for that destination type already registered. I'll leave this issue open and take a look.

[chaowlert]

Hi, I added Include command in Mapster 3.0 (https://github.com/chaowlert/Mapster/wiki/Config-inheritance), please try. Thx u.