NHibernate: Projecting child entities into parent properties throws an exception - nhibernate

Question

I have the following parent entity Department which contains a collection of child entities Sections
public class Department
{
private Iesi.Collections.Generic.ISet<Section> _sections;
public Department()
{
_sections = new HashedSet<Section>();
}
public virtual Guid Id { get; protected set; }
public virtual string Name { get; set; }
public virtual ICollection<Section> Sections
{
get { return _sections; }
}
public virtual int Version { get; set; }
}
public partial class Section
{
public Section()
{
_employees = new HashedSet<Employee>();
}
public virtual Guid Id { get; protected set; }
public virtual string Name { get; set; }
public virtual Department Department { get; protected set; }
public virtual int Version { get; set; }
}
I would like to transform (flatten) it to the following DTO
public class SectionViewModel
{
public string DepartmentName { get; set; }
public string SectionName { get; set; }
}
Using the following code.
SectionModel sectionModel = null;
Section sections = null;
var result = _session.QueryOver<Department>().Where(d => d.Company.Id == companyId)
.Left.JoinQueryOver(x => x.Sections, () => sections)
.Select(
Projections.ProjectionList()
.Add(Projections.Property<Department>(d => sections.Department.Name).WithAlias(() => sectionModel.DepartmentName))
.Add(Projections.Property<Department>(s => sections.Name).WithAlias(() => sectionModel.SectionName))
)
.TransformUsing(Transformers.AliasToBean<SectionModel>())
.List<SectionModel>();
I am however getting the following exception: could not resolve property: Department.Name of: Domain.Section
I have even tried the following LINQ expression
var result = (from d in _session.Query<Department>()
join s in _session.Query<Section>()
on d.Id equals s.Department.Id into ds
from sm in ds.DefaultIfEmpty()
select new SectionModel
{
DepartmentName = d.Name,
SectionName = sm.Name ?? null
}).ToList();
Mappings
public class DepartmentMap : ClassMapping<Department>
{
public DepartmentMap()
{
Id(x => x.Id, m => m.Generator(Generators.GuidComb));
Property(x => x.Name,
m =>
{
m.Length(100);
m.NotNullable(true);
});
Set(x => x.Sections,
m =>
{
m.Access(Accessor.Field);
m.Inverse(true);
m.BatchSize(20);
m.Key(k => { k.Column("DeptId"); k.NotNullable(true); });
m.Table("Section");
m.Cascade( Cascade.All | Cascade.DeleteOrphans);
},
ce => ce.OneToMany());
}
}
public class SectionMap : ClassMapping<Section>
{
public SectionMap()
{
Id(x => x.Id, m => m.Generator(Generators.GuidComb));
Property(x => x.Name,
m =>
{
m.Length(100);
m.NotNullable(true);
});
ManyToOne(x => x.Department,
m =>
{
m.Column("DeptId");
m.NotNullable(true);
});
}
}
But this throws a method or operation is not implemented.
Seeking guidance on what I am doing wrong or missing.

Answer 1

NHibernate doesn't know how to access a child property's child through the parent entity. A useful thing to remember about QueryOver is that it gets translated directly into SQL. You couldn't write the following SQL:
select [Section].[Department].[Name]
right? Therefore you can't do the same thing in QueryOver. I would create an alias for the Department entity you start on and use that in your projection list:
Department department;
Section sections;
var result = _session.QueryOver<Department>(() => department)
.Where(d => d.Company.Id == companyId)
.Left.JoinQueryOver(x => x.Sections, () => sections)
.Select(
Projections.ProjectionList()
.Add(Projections.Property(() => department.Name).WithAlias(() => sectionModel.DepartmentName))
.Add(Projections.Property(() => sections.Name).WithAlias(() => sectionModel.SectionName))
)
.TransformUsing(Transformers.AliasToBean<SectionModel>())
.List<SectionModel>();
I noticed in your comment you'd like an order by clause. Let me know if you need help with that and I can probably come up with it.
Hope that helps!

Answer 2

This may be now fixed in 3.3.3. Look for
New Feature
[NH-2986] - Add ability to include collections into projections
Not sure but if this is your problem specifically but if you are not using 3.3.3 then upgrade and check it out.
Aslo check out the JIRA

Answer 3

Have you tried a linq query like
from d in Departments
from s in d.Sections
select new SectionModel
{
DepartmentName = d.Name,
SectionName = s == null ? String.Empty : s.Name
}