c# AutoMapper ProjectTo selects all nested object properties - linq

Question

Let's take such classes:
public class Child
{
public int Id { get; set; }
public string Name { get; set; }
public string ExtraProp { get; set; }
}
public class Parent
{
public int Id { get; set; }
public string Text { get; set; }
public Child Child { get; set; }
public string ParentExtraProp { get; set; }
}
public class ChildVo
{
public int Id { get; set; }
public string Name { get; set; }
}
public class ParentVo
{
public int Id { get; set; }
public string Text { get; set; }
public ChildVo Child { get; set; }
}
Automapper mapping:
Mapper.CreateMap<Child, ChildVo>();
//.ForSourceMember(x => x.ExtraProp, o => o.Ignore()); //does not help
//.IgnoreAllNonExisting(); //does not help
Mapper.CreateMap<Parent, ParentVo>();
and query in Linq to Nhibernate:
var test = Session.Query<Parent>()
.Where(x => x.Id == myId)
.ProjectTo<ParentVo>()
.ToList();
ProjectTo selects only columns (properties) which are defined in ParentVo (not all properties from Parent class) - that's great. But is selects all columns (properties) from my Child class, despite the fact that they are not defined in ChildVo.
Why does Automapper ignore my nested property mapping? Is it possible to use all defined mappings during projection?

Answer 1

While I'm not familiar with nhibernate, the same test you've performed here works fine in Entity Framework. In EF you can see the query which has been generated before executing it - try doing this and seeing if it shows the additional column.
public class TestContext : DbContext {
public DbSet<Parent> Parents { get; set; }
}
var query = testContext.Parents.ProjectTo<ParentVo>();
Console.WriteLine(query.ToString());
This produces the following output (note no ExtraProp):
SELECT
[Extent1].[Id] AS [Id],
[Extent1].[Text] AS [Text],
CASE WHEN ([Extent2].[Id] IS NOT NULL) THEN 1 END AS [C1],
[Extent1].[Child_Id] AS [Child_Id],
[Extent2].[Name] AS [Name]
FROM [dbo].[Parents] AS [Extent1]
LEFT OUTER JOIN [dbo].[Children] AS [Extent2] ON [Extent1].[Child_Id] = [Extent2].[Id]
This makes me think that the problem is not AutoMapper specifically, but without seeing the generated query it's hard to tell.