May 30, 2013

Migrating from Castle ActiveRecord

Unfortunately Castle ActiveRecord project is abandoned and not developed anymore. Latest release uses NHibernate 3.0 and is not compatible with last NHibernate due  to the changes in API of dynamic proxy.

So we have decided to remove dead assembly and move on. In order to do that there some major steps that needed to be done:

  1. Rewrite all dependent code that used ActiveRecordMediator class
  2. Implement ISession, ISessionFactory lifetime management
  3. Reconfigure NHibernate without using AR wrappers over configuration
  4. Export existing AR mappings based on attributes to XML
  5. Migrate XML mappings to mapping by code

First two steps are tightly related. Methods in ActiveRecordMediator class are easily translated into appropriate analogs in ISession object. We already had a Repositories layer that was used to encapsulate all NHibernate related code, so it was not a really big problem to inject session to them.

For lifetime management we implemented same solution that was described in my blog earlier – let the IoC container resolve it.

Now about third step. NHibernate has not a lot of configuration in fact. All the new API descriptions can be found here. AR doesn’t add a lot, so nothing fancy here.

Export ActiveRecord mappings to XML

With exporting mappings things are starting to get interesting. I couldn’t find an out of the box way in AR to do that. So in fact I had to copy paste methods and to make something from AR public to support this. So here is a mapper class that allows exporting (btw AR sources that we have used before removing it). Line 21 is a place where you have map as a string and do anything you want with it.

Migration from hbm.xml to code

Sure you can stop migration here and just keep XML mappings. But that is just not good enough. Now there is a task of converting XML mappings to code. What is the best tool to covert XML to anything else?.. Well its XSLT. Sorry for that, but it is as it is. So I’ve created a transformation that is capable to do what is needed. Source is too long to put here, so I’m putting a link to appropriate gist. There are some preparations need for mappings – remove all nhibernate namespaces and wrappers like

<hibernate-mapping  auto-import="true" default-lazy="false" xmlns:xsd="" xmlns:xsi="" xmlns="urn:nhibernate-mapping-2.2">
    <!-- mapping here should be kept --> 

It uses XSLT 2.0 that is not supported by default .net tools. To run it you can use saxonica tool. In order to run it you can use following command line:

c:\Program Files\Saxonica\SaxonPE9.4N\bin\Transform.exe -s:mappings.xml -xsl:nbmToCs.xslt -o:mappings.cs

So after doing that you will have new nice mappings. Not everything that is supported by NHibernate is supported by XSLT, I’ve added only things that we needed. If you need to add something, feel free to contact me.

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