Use merge mappers for nested properties with entity framework core

[ilyasolofaa]

We use mapperly for merging Dto into EF Core Entities.
The target entities however may have other entities as navigation properties (virtual).
When using merger, those properties are using mappers, creating a new entity each time we merge.
This is upsetting an ef core change tracker and basically makes database to do work it should not.

An example:

	public partial class MyThingEntity
	{
		public Guid Id { get; set; }
		public string Name { get; set; }
		public virtual MyUserEntity? User { get; set; }
	}

	public partial class MyUserEntity
	{
		public Guid Id { get; set; }
		public string Email { get; set; }
	}

	public interface IMyThingUpdate
	{
		Guid Id { get; set; }
		string Name { get; set; }
		IUpdateUser User { get; set; }
	}

	public interface IUpdateMyUser
	{
		Guid Id { get; }
		string Email { get; }
	}

	[Mapper(PropertyNameMappingStrategy = PropertyNameMappingStrategy.CaseInsensitive, AllowNullPropertyAssignment = false, EnumMappingIgnoreCase = true)]
	public static partial class MyEntityMergeMappers
	{
		public static partial void MergeToMyThingEntity(this IMyThingUpdate source, MyThingEntity destination);
		public static partial void MergeToMyUserEntity(this IUpdateMyUser source, MyUserEntity destination);
	}

Generate code for public static partial void MergeToMyThingEntity():

    public static partial class MyEntityMergeMappers
    {
        [global::System.CodeDom.Compiler.GeneratedCode("Riok.Mapperly", "4.1.1.0")]
        public static partial void MergeToMyThingEntity(this global::ConnektAPI.Domain.Entities.IMyThingUpdate? source, global::ConnektAPI.Domain.Entities.MyThingEntity? destination)
        {
            if (source == null || destination == null)
                return;
            destination.Id = source.Id;
            if (source.Name != null)
            {
                destination.Name = source.Name;
            }
            if (source.User != null)
            {
                destination.User = MapToMyUserEntity(source.User);
            }
        }

        [global::System.CodeDom.Compiler.GeneratedCode("Riok.Mapperly", "4.1.1.0")]
        public static partial void MergeToMyUserEntity(this global::ConnektAPI.Domain.Entities.IUpdateMyUser? source, global::ConnektAPI.Domain.Entities.MyUserEntity? destination)
        {
            if (source == null || destination == null)
                return;
            destination.Id = source.Id;
            if (source.Email != null)
            {
                destination.Email = source.Email;
            }
        }

        [global::System.CodeDom.Compiler.GeneratedCode("Riok.Mapperly", "4.1.1.0")]
        private static global::ConnektAPI.Domain.Entities.MyUserEntity MapToMyUserEntity(global::ConnektDataObjects.IUpdateUser source)
        {
            var target = new global::ConnektAPI.Domain.Entities.MyUserEntity();
            target.Id = source.Id;
            if (source.Email != null)
            {
                target.Email = source.Email;
            }
            return target;
        }
    }

As we can see, the merge will sue mapper to CREATE a new entity and there doesn't seem to be any way to specify that certain property need to be also merged?
Is there any other way besides writing a custom mapper manually?

[latonz]

Seems to be a duplicate of #1311