AutoMapper Project().To() and sorting a child collection

Question

I have an object graph that I'm loading from a database using EF CodeFirst and AutoMapper into DTOs:-

public class Foo
{
  public int Id { get; set; }
  public virtual ICollection<Bar> Bars { get; set; }
}

public class Bar
{
  public int Id { get; set; }
  public int FooId { get; set; }
  public virtual Foo Foo { get; set; }

  public string Name { get; set; }
  public int SortOrder { get; set; }
}

public class FooDto
{
  public IEnumerable<BarDto> Bars { get; set; }
}

public class BarDto
{
  public string Name { get; set; }
  public int SortOrder { get; set; }
}

My mappings look like:-

mapper.CreateMap<Foo, FooDto>();
mapper.CreateMap<Bar, BarDto>();

So far, so good. I can grab the entities from my context and project to the DTO nicely:-

var foos = context.Foos.Project().To<FooDto>();

What I can't do with this approach, however, is sort the Bars by their SortOrder inside the IQueryable.

If I try:-

mapper.CreateMap<Foo, FooDto>()
  .ForMember(
    x => x.Bars
    opt => opt.MapFrom(src => src.Bars.OrderBy(x => x.SortOrder)));
mapper.CreateMap<Bar, BarDto>();
var foos = context.Foos.Project().To<FooDto>();

I get an exception:-

System.InvalidOperationException: Sequence contains no elements
  at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
  at AutoMapper.MappingEngine.CreateMapExpression(Type typeIn, Type typeOut)
  ...

Seems this is related to https://github.com/AutoMapper/AutoMapper/issues/159 - though I'm already using a complex type for the child collection. I guess CreateMapExpression doesn't support OrderBy on child collections?

If I'm not using .Project().To() then I can sort the child collection easily:-

var model = context.Foos.Select(x => new FooDto()
{
  Bars = x.Bars.OrderBy(y => y.SortOrder)
});

but then I have to repeat the mapping wherever I want to use it, defeating the purpose of using AutoMapper.

Curiously:-

1) I can perform other (more complicated?) operations on the child collection and flatten those into my parent DTO no problem:-

mapper.CreateMap<Foo, FooDto>()
  .ForMember(
    x => x.AllBarsHaveAName,
    opt => opt.MapFrom(src =>
      src.Bars.All(x => x.Name != null)));

2) I can Mapper.Map<FooDto>(foo); in memory just fine, and it'll sort the bars no problem.

It's possible to sort the child collection at the IQueryable level while still using .Project().To()?

Answer 1

Ended up modifying the AutoMapper source code to support this scenario. Hopefully the proposed fix will be accepted, but in the meantime you can see the details at:-

https://github.com/AutoMapper/AutoMapper/pull/327