Serializing DTO's over WCF - wcf

Question

I have a problem with NHibernate for a longtime which I solved by non-optimal ways/workarounds.
First of all, I'm using WCF REST to communicate with my client application. As you know, serializing persisted entities is not a best practise and always causes other problems. Thus, I always map my entities to DTO's with NHibernates Transformers. The problem is that I have entities which are more complex to use Transformers to convert them.
How can I map sub entities to sub dto's by using transformers or any other nhibernate feature?
Note: I don't want to use 3rd parties like Automapper.
These are the Entities and DTO's which I want to map. Variable names are exactly same with each other.
Entity Classes:
EntityType
public class crmEntityType : EntityModel<crmEntityType>
{
public crmEntityType()
{
Association = new List<crmEntityType>();
Fields = new List<crmCustomField>();
}
public virtual int ID { get; set; }
public virtual string Title { get; set; }
public virtual ICollection<crmEntityType> Associations { get; set; }
public virtual ICollection<crmCustomField> Fields { get; set; }
}
CustomFields
public class crmCustomField : EntityModel<crmCustomField>
{
public virtual int ID { get; set; }
public virtual string Name { get; set; }
public virtual crmEntityType EntityType { get; set; }
}
DTO's
EntityTypeDTO
[DataContract]
public class EntityTypeDTO
{
[DataMember]
public int ID { get; set; }
[DataMember]
public string Title { get; set; }
[DataMember]
public IList<CustomFieldDTO> Fields { get; set; }
[DataMember]
public int[] Associations { get; set; }
}
CustomFieldDTO
[DataContract]
public class CustomFieldDTO
{
[DataMember]
public int ID { get; set; }
[DataMember]
public string Name { get; set; }
[DataMember]
public int EntityType { get; set; }
[DataMember]
public int FieldType { get; set; }
}

Answer 1

I found my solution by spending my day and night to work it out. Finally, I've got the best solution I could find. I hope it helps someone in my condition some day.
This linq query works with just one database round-trip. I think it maps the classes in memory.
return (from entityType in Provider.GetSession().Query<crmEntityType>()
.Fetch(x => x.Association)
.Fetch(x => x.Fields)
.AsEnumerable()
select new EntityTypeDTO()
{
ID = entityType.ID,
Title = entityType.Title,
Association = entityType.Association.Distinct()
.Select(asc => asc.ID).ToArray<int>(),
Fields = entityType.Fields.Distinct()
.Select(fi => new CustomFieldDTO
{ ID = fi.ID,
Name = fi.Name,
Value = fi.Value,
EntityType = fi.EntityType.ID,
Type = fi.Type
}).ToList()
}).ToList();