Learning by doing

Lately, it feels like I've been wading through mud. As if the ActiveRecord library has been doing nothing but preventing me from getting my work done. In my dreams, I could call MyEntity.Find() with a list of ICriterion objects, and get back what I want. I was having problems with that, because I want to select several object, left joining to a notes table, and return only the most recent note (with max(NoteDate)). While I can think it, and write it in raw SQL, it has been tough doing this in an ActiveRecord query. Just to see if it is possible, I tried HQL, and finally resorted to raw SQL. I learned that "raw SQL" has several requirements imposed on it: * The returned result set must include the complete field list of all entities that you want to return (as far as I can tell). * NHibernate will replace {nt.*} with a complete field list if you include "nt" as an alias for typeof(MyNote). * Do not list an alias unless you are returning that entity in your ...

Update May 25, 2007: ActiveRecord now supports DetachedCriteria, which eliminates the need for the SlicedFindAll that I wrote below. It is nice when a library moves to add support for such commonly needed functions. So in summary, use Detached criteria instead of the code below. It is still a nice example of using NHibernate sessions. I have a history log, where each history record "belongs to" a service record. I have to treat this as a child-to-parent join, since some children are orphans. I wanted to use the FindAll(Criteria), but I wanted the option to have optional criteria, orders and aliases. My solution was to create an ARAlias class to represent an Associated Entity and an alias, and then build an ARBusinessBase class with the following method: public static T[] SlicedFindAll(int firstResult, int maxResults, Order[] orders, ARAlias[] aliases, params ICriterion[] criteria) { IList list = null; ISessionFactoryHolder holder = ActiveRecordMediator.GetSessionF...

While looking for Castle ActiveRecord examples, I found a blog by David Hayden - post 1 (design pattern overview) , post 2 (some details on a possible implementation) and post 3 (using the Castle Project). David had a series of articles about Rocky Lhotka's .NET Business Objects (one for each chapter), which I have also read and tried to apply. Don't get me wrong, Rocky's CSLA library works, but as of .Net 1.1 it required a great deal of code on my part. There are reasons why I and many others were investigating code generation tools. I have been studying Castle's ActiveRecord framework for a week and a half, and it is awesome for new development and clean data. During this discussion, remember that ActiveRecord mostly generates the XML mapping files for you and delegates the heavy lifting to NHibernate . If you have a legacy database with "sometimes there" keys, the framework will punish you severely. Below is an example of a legacy scenario that wi...

Since this is my first post on the subject, let me introduce the Castle project - a .Net framework that I have been exploring recently. It has a project that tries to mimic ActiveRecord in Ruby-On-Rails, although the Castle version of ActiveRecord uses NHibernate. The good news is that an ActiveRecord class doesn't require any XML configuration or mapping files. The somewhat bad news is that you DO have to declare your classes and populate them with properties, private members and AR mapping attributes. Since I will probably use SQLServer 2000, I will just write a few queries to extract the data type and field list for each table that I want to support. More on this later. For today, I wanted to extract the class-to-database mapping information that Castle's ActiveRecords feeds to NHibernate. I finally looked through the source code a bit and after a blind alley (NHibernate.Cfg Configuration is mostly for database connections), I ran across the ActiveRecordModel class...