NHibernate mapping with enum

When mapping a property of an enumeration type you should always set the type attribute of that property in the mapping file to that enumaration type.

Often you don't set the type at all or you set it to Int32 since your enum is represented as an int in the database. It's easy to assume that setting the attribute type to Int32 will have the same effect as using the enum type. And it will work!

When using an In32 your code will execute without exception. The field will be selected and updated as usual.
However, during the session flush nhibernate will recognize that the current value of the property differs from the originall value causing an update to the database. Another disadvantage is that the query cache for this class won't work either.

Using Fiddler on localhost

Fiddler is a great tool to analyse http traffic to the server. But it's sometimes difficult to make it work on localhost. But if you enter a simple dot (.) after "localhost" in the url it works.

So intead of http://localhost:8081/...,
use http://localhost.:8081/...

Reference:
http://weblogs.asp.net/lorenh/archive/2008/01/10/tip-for-using-fiddler-on-localhost.aspx

NHibernate: Enable second level cache using MemCached

The second level cache is a powerful feature used by NHibernate to cache objects and queries to limit the number of database queries.

NHibernate uses a provider based architecture where cache providers can be plugged in using the config file.

NHibernate is shipped with several cache providers, example:
- SysCache (uses ASP.NET Cache Objects to cache data)
- MemCached (distributed in-memory Cache running as a separate Windows Service)

We will use MemCached in this example.

There are several win32 ports of MemCached available. We will use one available at:
http://jehiah.cz/projects/memcached-win32/

Start by downloading MemCached from the URL above and from a Command prompt type:
memcached -d install <enter>
memcached -d start <enter>
This will start the MemCached service on your computer.

Next, we will configure MemCached in your application. Add a new configuration settings in your config file under <configSettings>:
<section name="memcache" type="NHibernate.Caches.MemCache.MemCacheSectionHandler,NHibernate.Caches.MemCache" />

Add the MemCached settings using:
<memcache>
<memcached host="192.168.1.0" port="11211" weight="1"/>
</memcache>

The next step is to enable caching in your NHiberate project. Under the <NHibernate> node, add the following application settings:
<add key="hibernate.cache.provider_class" value="NHibernate.Caches.MemCache.MemCacheProvider,NHibernate.Caches.MemCache" />
<add key="hibernate.cache.use_query_cache" value="true"/>
<add key="expiration" value="120" />

At last we need to enable caching for the persistant classes in your application. This is done in the hbm.xml file using the <cache> element:
<class name="NameSpace.Class, NameSpace" table="tblInDb">
<cache usage="read-write"/>
...
</class>

To enable caching for relations, add the <cache> element for each relation:
<bag name="Childs" lazy="true">
<cache usage="read-write"/>
<key column="ParentId"/>
<one-to-many class="NameSpace.ChildClass, NameSpace"/>
</bag>


The second level cache is used by NHibernate in the following scenarios:
- Single objects retrieved using ISession.Load
- Lists of objects retrieved using IQuery.List (if hibernate.cache.use_query_cache is set to true)
- Relational objects (when the bag is marked with <cache>)

Note that NHibernate does not use the second level cache when using ICriteria.