gistfile1.cs

// interfaces

public interface IResult<T>
{
	T GetResult();
}

public interface IEntityQuerier
{
	void Execute(ISession session, Guid parameter);
}

public interface IEntityResult<TEntity> : IResult<TEntity>, IEntityQuerier where TEntity : PersistentObject { }

// abstract base

public abstract class HqlQuerierBase<TResult> : IEntityResult<TResult> where TResult : PersistentObject
{
	private TResult _result;

	public void SetResult(TResult result)
	{
			_result = result;
	}

	public TResult GetResult()
	{
		return _result;
	}

	public void Execute(ISession session, Guid parameter)
	{
		_result = ExecuteCore(session, parameter);
	}

	protected virtual TResult ExecuteCore(ISession session, Guid parameter)
	{
		return session.CreateQuery(GetHql())
			.SetParameter("id", parameter)
			.SetResultTransformer(new DistinctRootEntityResultTransformer())
			.UniqueResult<TResult>();
	}

	protected abstract string GetHql();
}

// impl

public class PaymentHistoryQuery : HqlQuerierBase<Customer>
{
	protected override string GetHql()
	{
		return
			@"from Customer c 
				left join fetch c.PaymentHistory ph 
				left join fetch ph.Payment 
				where c.id = :id";
	}

        public static implicit operator PaymentHistoryQuery(Customer customer)
	{
		var query = new PaymentHistoryQuery();
		query.SetResult(customer);
		return query;
	}
}