Automapper null properties

问题:

I map my objects to dtos with Automapper.

public class OrderItem : BaseDomain
{
    public virtual Version Version { get; set; }
    public virtual int Quantity { get; set; }
}




[DataContract]
[Serializable]
public class OrderItemDTO
{
    [DataMember]
    public int Id { get; set; }
    [DataMember]
    public string Guid { get; set; }
    [DataMember]
    public virtual int? VersionId { get; set; }
    [DataMember]
    public virtual string VersionName { get; set; }
    [DataMember]
    public virtual int Quantity { get; set; }

}

So when I have OrderItem with null version, i get an exception at:

 Mapper.Map<OrderItem, OrderItemDTO>(item)

 Missing type map configuration or unsupported mapping.

回答1:

Without having seen your mapping code it is hard to say exactly what is going wrong but my guess is that you are mapping your types with code similar to the following:

Mapper.CreateMap<OrderItem, OrderItemDTO>()
      .ForMember(dest => dest.VersionId, options => options.MapFrom(orderitem => orderitem.Version.VersionId))
      .ForMember(dest => dest.VersionName, options => options.MapFrom(orderitem => orderitem.Version.VersionName))
      ;

The code above will fail when OrderItem.Version is null. To prevent this you can check for null in the delegates passed to ForMember:

Mapper.CreateMap<OrderItem, OrderItemDTO>()
      .ForMember(dest => dest.VersionId, options => options.MapFrom(orderitem => orderitem.Version == null ? (int?) null : orderitem.Version.VersionId))
      .ForMember(dest => dest.VersionName, options => options.MapFrom(orderitem => orderitem.Version == null ? null : orderitem.Version.VersionName))
      ;