How to resolve 'Nullable object must have a value' error in Automapper and EF Core?

Question

I am working on a Blazor Server application in which I added a new nullable field called ShippingWeek to an entity called OrderDetail. However, when I try to use Automapper to map an Order entity to its corresponding OrderDto entity, I get a System.InvalidOperationException: Nullable object must have a value error. Here's the code I'm using in OnInitializedAsync:

IQueryable<OrderDto?> _ordersDto = Mapper.ProjectTo<OrderDto>(_order);

And here's the relevant portion of the Automapper profile:

CreateMap<Order, OrderDto>()
    .ForMember(dest =>
            dest.OrderDetailsDto,
        opt => opt.MapFrom(src => src.OrderDetails))
    .ForMember(dest =>
            dest.Customer,
        opt => opt.MapFrom(src => src.Customer))
    .ForAllMembers(opts =>
    {
        opts.Condition((src, dest, srcMember) => srcMember != null);
    });

How can I resolve this error and use Automapper to map the two entities correctly?

Answer 1

Here is how I fixed.

CreateMap<Order, OrderDto>()
    .ForPath(dest =>
            dest.OrderDetailsDto,
        opt => opt.MapFrom(src => src.OrderDetails))
    .ForMember(dest =>
            dest.Customer,
        opt => opt.MapFrom(src => src.Customer))
    .ForAllMembers(opts =>
    {
        opts.PreCondition((src, dest, srcMember) => srcMember != null);
    });

Answer 2

Hello Cenk

One way to resolve this issue is to use PreCondition instead of Condition in your AutoMapper profile. PreCondition checks the condition before the mapping operation, whereas Condition checks after the source value has been resolved. This means that if the PreCondition is not met, AutoMapper will not attempt to map the property, avoiding the Nullable object must have a value error.

CreateMap<Order, OrderDto>()
    .ForMember(dest =>
            dest.OrderDetailsDto,
        opt => opt.MapFrom(src => src.OrderDetails))
    .ForMember(dest =>
            dest.Customer,
        opt => opt.MapFrom(src => src.Customer))
    .ForAllMembers(opts =>
    {
        opts.PreCondition((src, dest, srcMember) => srcMember != null);
    });