NHibernate QueryOver Could not resolve property

Question

I'm trying to QueryOver and select a property which returns a private property. I can't explain it well but the example will tell you.

Mapping:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" namespace="IWA.Model" assembly="IWA.Model">
<class name="Test" lazy="false" table="Test">

<id name="Id" column="Id" >
  <generator class="identity" />
</id>

<bag name="_images" access="field" table="Image" cascade="none">
  <key column="IdTest" />
  <one-to-many class="Image" />
</bag>

</class>
</hibernate-mapping>

Class:

public class Test : IEntity<int>
{
    private readonly IList<Image> _images;

    public Test()
    {
        _images = new List<Image>();
    }

    public int Id { get; set; }


    public Image Image => _images.FirstOrDefault();
}

QueryOver:

TestDto r = null;
Session.QueryOver<Test>()
            .Where(x => x.Id == _id)
            .Select(
                Projections.Property<Test>(x => x.Id).WithAlias(() => r.Id),
                Projections.Property<Test>(x => x.Image).WithAlias(() => r.Image)
            )              .TransformUsing(Transformers.AliasToBean<TestDto>())
            .SingleOrDefault<TestDto>();

When I try this query I get 'Could not resolve property'. Querying without projections works fine.

Any idea what I am doing wrong ??

Answer 1

NHibernate cannot resolve an un-mapped, runtime computed property such as Image , and thus it cannot project it. You can only use mapped properties in projections.

For achieving your projection, you have to join on your Image table and only Take(1) . See this for an example.