Firstly, lets look at simplified description of the problem. Those using MySQL have the luxury of limit, which makes paging data sets a breeze, but in SQL Server(and Oracle) things get a bit more “tricky”. The trick is to count the rows on the result set, using RowCount over something, and mix that in with a sub query, but there is a problem with nHibernate T-SQL 2005 Dialect. The RowCount was being used on the sub-query, and not the parent query. Now that I had discovered the problem.

“ROW_NUMBER() OVER(ORDER BY CURRENT_TIMESTAMP) as __hibernate_sort_row” is in the wrong place!

After some research, I found that other people were having this problem too. Marcin Daczkowski has an excellent work-around, that he blogged about, he also describes the problem with some NH generated SQL examples, I won’t repeat myself here, so have a look at his post if you are not sure and check his bug report here.

I found a another solution here too- not sure this one works though, ultimately I had to come up with a solution that suited my project.

There are some reasons why I can’t use Marcin Daczkowski solution.

– Firstly, it does not look like the guys at nHibernate be able to release the patched version of nHibernate any time soon,I guess they are very busy working hard on version 3.0! Can’t wait for that realease! see the comments here.

– Secondly, if I build my own version of nHibernate, I will need to also rebuild all my dependencies, linking them with Marcins patched version. That means FluentNHibernate needs to be rebuilt, NHibernate.Caches.SysCache needs to be rebuilt, NHibernate.ByteCode.Castle needs to be rebuilt, you get the picture?

So after some thought and source code investigation, I came up with the idea of making a customised Dialect, and just use Darcins patched files. Now, I don’t need to build a patched version of my all my open source dependencies, as I have my own SQL dialect set up in the fluent configuration.


_sessionFactory = Fluently.Configure()
      .Database(MsSqlConfiguration
      .MsSql2008
      .ConnectionString(connectionString)
      .CurrentSessionContext("web")
      .Dialect(CustomSQL2008Dialect)
)


My Dialect classes are set up like this:


public class CustomSQL2008Dialect: CustomSQL2005Dialect {
      public GWMsSql2008Dialect () {
            // Duplicate of the contents of MsSsql2008Dialect constructor goes here
      }
}

public class CustomSQL2005Dialect: MsSql2000Dialect {
      // the contents Darcins MsSql2005Dialect file goes here.
      // MsSql2005Dialect at NHibernate JIRA
}


Luckily, I have unit tests set up for all my repository methods, and after seeing the green bar in NUnit, I was more than satisfied with the custom dialect. I hope the guys at NHibernate manage to get things working in their next release, keep up the good work guys! And a special thanks to
to Darcin, for writing the patch.

Here is a copy the Custom Sql 2008 Dialect.

FNH extends NHibernate, and automagically generates XML mapping files for your objects. Unfortunately, to get stored procedures to work, you need to take a step backwards, and create good old fashioned hbm.xml files, doing the mappings manually.

Firstly , let us look at the results of the stored procedure that we want to map.

The class that will use this data is called lookup.

The code for this class is:

 
This object will be used to populate a simple drop down list, so that a user can select their county.

When I started using FluentHNibernate, I wanted to totally avoid using XML mappings, so I skipped chapters 3 and 6 of Hibernate in Action. My first mistake! So for those attempting this, it may be worth your while understanding Hibernate mappings before you proceed. (You may also ask why I have the Java Book and my code is in C#, that is because I am quite used to working in different programming languages, so those who prefer examples in .Net examples check NHibernate in Action.)

Let’s move on to creating the mapping file.

IMPORTANT: When you add the mapping file to your project, make sure you set the Build Action to Embedded Resource!

I have created a Lookup.hbm.xml file, and the source is below:

To put it quite simply, lines 5 to 13 map my Lookup class to the columns in the stored procedure, while lines 16 to 20 map the results from the stored procedure my lookup class. Line 22 names the stored procedure. I am not sure if this is the best way to achieve the mappings, so any feedback would be appreciated.

Once your object is nicely mapped, you then need to update your fluent configuration. All you need to do is tell FNH to load hbmMappings from the current assembly. See the snippet below:

To retrieve the list of lookups, I do the following, which populates my results variable with a list of all my lookups.

And that is it, the results variable now contains the list of lookups that I can use to populate my list control.

(i’ve used code sections to create more sections.)

Let's say we have a bit field called "isActive" which holds 0 if the user is inactive and 1 if he/she is active. For our presentation we just want one button in order to achieve this state change and the underlying DB access should be done with one SQL statement if possible. Okay so here we go:

Voila thats it, this SQL query toggles the isActive field of the user by using bitwise negation. The current state is being deducted from 1 and therefore 1 minus 0 results in 1 and 1 minus 1 in 0. Invert done! Needless to say, this solution is not limited to SQL and can be used everywhere where negation is needed.

I enjoy this solution because it's so handy. have fun!