NHibernate SetResultTransformer and DTO

Lately I have been exploring NHibernate and ICriteria. NHibernate is great I would recommend it to anyone but often I find the documentation and examples are hard to follow.

I found an interesting article by Max Andersen on Criteria Transformers for Hibernate but of course it applies to NHibernate as well. I tried it out and it worked well.

It’s really easy with NHibernate to select a simple typed list of results

For example:

    public static IList List() 
        ICriteria criteria = Persistence.Session.CreateCriteria(typeof(Profile)); 
        return criteria.List(); 

But how about when your HQL or ICriteria selects across multiple classes or entities. For example you may have an class Profile that has a many to one relationship with an class Department.

Your SQL would be like:

SELECT p.ItemID, p.Name, p.Summary, d.ItemID, d.Name
FROM Profile p inner join Department d on p.DepartmentID = d.ItemID

First we need to create a class to hold the result of our query. Below I have created a DTO or Data Transfer Object which combines the properties from the Profile and Department classes that I require.

    public class ProfileDTO 
        private int _itemID; 
        private int _departmentID; 
        private string _departmentName; 
        private string _name; 
        private string _summary; 
        public virtual int ItemID 
            get { return _itemID; } 
            set { _itemID = value; } 
        public virtual int DepartmentID 
            get { return _departmentID; } 
            set { _departmentID = value; } 
        public string DepartmentName 
            get { return _departmentName; } 
            set { _departmentName = value; } 
        public string Name 
            get { return _name; } 
            set { _name = value; } 
        public string Summary 
            get { return _summary; } 
            set { _summary = value; } 

From here we can create a query that returns a Generic list of ProfileDTO.

    public static IList List() 
        ICriteria criteriaSelect = Persistence.Session.CreateCriteria(typeof(Profile)); 
            .Add(Projections.Property("ItemID"), "ItemID"
            .Add(Projections.Property("Name"), "Name"
            .Add(Projections.Property("Summary"), "Summary"
            .Add(Projections.Property("d.ItemID"), "DepartmentID"
            .Add(Projections.Property("d.Name"), "DepartmentName")); 
        return criteriaSelect.List(); 

NHibernate SetResultTransformer combined with the generic list make returning a typed list from a complicated query really easy.