I have been working with NHibernate for manner of couple of years and I never seriously thought about how it is built from inside, what is the architecture of NH, how much it depends on ADO.NET, how they made reflection to work fast, how high code quality is, which people worked on it and what was the history of it. The other day, I had chance to start mine own small ORM project and all of this questions raised for me. Thus I will do my best to share everything I discovered in NHibernate surgery.

1. Kiev ALT.NET
NHibernate from inside
by Andriy Buday

2. NHibernate guts. Why?
Because… it is fun… interesting…
http://andriybuday.com | http://kievalt.net

3. NHibernate guts. Why?
And not so scary as you could have thought
http://andriybuday.com | http://kievalt.net

4. Outline
 Q1: If build similar ORM ourselves?
 Q2: How does it look like at glance?
 History
 Community
 Code base quality
 Q3: Dive deeper?
 Main interaction classes
 DEMO 1: Debugging fetch logic
 DEMO 2: Debugging save logic
Let see… if guts could be interesting o_O
http://andriybuday.com | http://kievalt.net

5. Q1: If build similar ORM ourselves?
Lets draw…
http://andriybuday.com | http://kievalt.net

6. Q1: If build similar ORM ourselves?
This might be the solution we came up with…
Even uglier than real cave drawing 
http://andriybuday.com | http://kievalt.net

7. Q2: How does it look like at glance?
History
http://andriybuday.com | http://kievalt.net

8. Q2: How does it look like at glance?
Community
http://andriybuday.com | http://kievalt.net

9. Q2: How does it look like at glance?
NDepend analysis
http://andriybuday.com | http://kievalt.net

10. Q2: How does it look like at glance?
NDepend analysis: Application Metrics
L. of code : 62,914 Fields : 7,205
L. of comment: 37,113 C# source files : 1,437
Assemblies : 3 IL instruction : 437,982
Namespaces : 90 Classes : 1,866
Types : 2,211 UT coverage: 75.93%
Methods : 18,335
http://andriybuday.com | http://kievalt.net

11. Q2: How does it look like at glance?
Architecture: entity states
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12. Q2: How does it look like at glance?
Architecture: more
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13. Q2: How does it look like at glance?
Personal opinion: really well-commented
/// <summary>
/// Get the alias of the entity encapsulated by this criteria instance.
/// </summary>
/// <value>The alias for the encapsulated entity.</value>
string Alias { get; }
/// <summary>
/// Was the read-only mode explicitly initialized?
/// </summary>
/// <returns><c>true</c> if the read-only mode was explicitly initialized, otherwise <c>false</c>.</returns>
/// <seealso cref="ICriteria.SetReadOnly(bool)" />
/// <seealso cref="ICriteria.IsReadOnly" />///
bool IsReadOnlyInitialized { get; }
/// <summary>
/// Will entities (and proxies) loaded by this Criteria be put in read-only mode?
/// </summary>
/// <remarks>
/// <para>
/// If the read-only setting was not initialized, then the value of the session's
/// <see cref="ISession.DefaultReadOnly" /> property is returned instead.
/// </para>
/// <para>
/// The read-only setting has no impact on entities or proxies returned by the
/// Criteria that existed in the session before the Criteria was executed.
/// </para>
/// </remarks>
/// <returns>
/// <c>true</c> if entities and proxies loaded by the criteria will be put in read-only mode,
/// otherwise <c>false</c>.
/// </returns>
/// <seealso cref="ICriteria.SetReadOnly(bool)" />
/// <seealso cref="ICriteria.IsReadOnlyInitialized" />
bool IsReadOnly { get; }
/// <summary>
/// Used to specify that the query results will be a projection (scalar in
/// nature). Implicitly specifies the projection result transformer.
/// </summary>
/// <param name="projection">The projection representing the overall "shape" of the
/// query results.</param>
/// <returns>This instance (for method chaining)</returns>
/// <remarks>
/// <para>
/// The individual components contained within the given <see cref="IProjection"/>
/// determines the overall "shape" of the query result.
/// </para>
/// </remarks>
ICriteria SetProjection(params IProjection[] projection);
Don’t read code – see how green it is 
http://andriybuday.com | http://kievalt.net

14. Q2: How does it look like at glance?
Personal opinion: a lot of noise in code
if (cmd.Connection != null)
{
// make sure the commands connection is the same as the Sessions connection
// these can be different when the session is disconnected and then reconnected
if (cmd.Connection != sessionConnection)
{
cmd.Connection = sessionConnection;
}
}
else
{
cmd.Connection = sessionConnection;
}
Now read code!
Don’t you think it can be replaced?
cmd.Connection = sessionConnection;
http://andriybuday.com | http://kievalt.net

15. Q3: Dive deeper?
Lets have some fun with code & debugging…
http://andriybuday.com | http://kievalt.net

16. Q3: Dive deeper?
Lets have some fun with code & debugging…
 Overview
 DEMO 1: Debugging fetch
 DEMO 2: Debugging save
http://andriybuday.com | http://kievalt.net

17. Questions?
Ask me something! But easy!
http://andriybuday.com | http://kievalt.net

18. Read blog! Follow me! Visit KIEV ALT.NET!
http://andriybuday.com/
@andriybuday
andriybuday@gmail.com
http://kievalt.net/
http://andriybuday.com | http://kievalt.net

19. Links
 My blog:
 http://andriybuday.com
 Kiev ALT.NET:
 http://kievalt.net/
 NHibernate:
 Home Page: http://nhforge.org/
 Source Code: https://github.com/nhibernate/nhibernate-core
 Screencasts: http://www.summerofnhibernate.com/
 Reference: http://www.nhforge.org/doc/nh/en/index.html
 NDepend analysis:
http://www.ndepend.com/SampleReports/OnNHibernate/NDependReport.html
 So what’s NH development look like: http://elegantcode.com/2008/12/07/so-
whats-nhibernate-development-like/
 Mapping by code:
 http://fabiomaulo.blogspot.com/2011/04/nhibernate-32-mapping-by-code.html
http://andriybuday.com | http://kievalt.net