ProjectToType throws when nullable navigation maps to record DTO with non-nullable value type

[unzeitip]

First of all, thank you for Mapster — it's been a great fit for our project and we really appreciate the work you've put into it.

I've run into what looks like a bug with ProjectToType when mapping a nullable navigation property to a record DTO that has non-nullable value type parameters. Here I provide additional context if it helps track this down.

Mapster version: 10.0.6
EF Core version: 10.0.5

Minimal reproduce

// Entities:
public class OrderEntity
{
    public int Id { get; set; }
    public int? CodId { get; set; }
    public OrderCodEntity? Cod { get; set; }
}

public class OrderCodEntity
{
    public int Id { get; set; }
    public long Value { get; set; }
}

// DTOs:
public record OrderDto(int Id, OrderCodDto? Cod);
public record OrderCodDto(long Value);

// Mapping + query:
TypeAdapterConfig<OrderEntity, OrderDto>.NewConfig();
TypeAdapterConfig<OrderCodEntity, OrderCodDto>.NewConfig();

var results = dbContext.Orders
    .ProjectToType<OrderDto>()
    .ToList();  // throws when any Order has Cod == null

// Seed data:
new OrderEntity { Id = 1, Cod = new OrderCodEntity { Value = 42L } }  // OK
new OrderEntity { Id = 2, Cod = null }                               // causes crash

Expected behavior

OrderDto(1, OrderCodDto(42))
OrderDto(2, null)

Actual behavior

System.InvalidOperationException: Nullable object must have a value.

Workaround

   .Map(
       d => d.Cod,
       s => s.Cod == null ? null : new OrderCodDto(s.Cod.Value)
   );

Note

The issue persists when using Mapster.EFCore 10.0.6 and calling EFCoreProjectToType<OrderDto>() instead of ProjectToType<OrderDto>() - same exception is thrown.

[DocSvartz]

Hi @unzeitip.

Does this error exist when using?

Mapster version: 10.0.4-a
EF Core version: 10.0.0

[DocSvartz]

@unzeitip It's weird, but in your example I get a different error: System.NullReferenceException: Object reference not set to an instance of an object.
and apparently this doesn't work in version 7.4.0 either.

[unzeitip]

@DocSvartz I'm getting the exact error as in the issue:

And yes, the error still occurs with:

• Mapster 10.0.4-a
• EF Core 10.0.0

[DocSvartz]

This is related to mapping on the constructor and partly due to how EFCore insert and load related entities.

In source type doesn't have a Nullable value type anyway. So where this error comes from is completely unclear 😅