Monday, April 9, 2007

ORM:1, Hand Coding:0

By definition I am lazy, I love using tools to reduce my workload. Object Relational Mapping (ORM) is one of those tools that I can not live without.

Several projects ago we decided that it would be better if we generate at least 85% of persistence layer automatically, but still would have control of how and when do we use ORM. NHibernate was our choice of the ORM (at time it was beta 0.8).

So why does ORM rule? Well, I would like to share a great story on how we were able to leverage NHibernate. On one of my current projects we are using NHibernate (1.03 beta) to generate the persistence layer for the use with Oracle 10G R2.
As we were reviewing and finalizing the requirements for purchasing production hardware and licenses, the client’s newly hired CIO, asked us: “why do we need to have both Oracle and SQL Server?” Of course we answered that: “we are using Oracle because it is your preferred choice of database to persist application data. SQL Server is a requirement for the BizTalk 2006, which we are using as a middleware server.”
The next question was: “What will it take to switch to SQL Server completely?” I should mention this conversation took place half way through our development effort. Our response was: “since we are using ORM to abstract the database from the application, it should only take 54 hours.”
Here is a list of tasks we had to do:
1. SQL Server Setup (Total Effort: 4 hours)
2. Database Conversion (Total Effort: 24 hours)
a) re-create 135+ tables from the Database Definition Language (DDL) scripts;
b) make unit conversion updates like: Change VARCHAR2 to VARCHAR, CLOB to VARCHAR(MAX), NUMBER to BIGINT, NUMBER (1) to BIT/BOOLEAN
c) update defaults, identities
d) update naming conventions
e) update DDL Script that generates triggers
f) update 5 stored procedures and functions
3. Code Updates (Total Effort: 10 hours)
a) Update the NHibernate XML Mapping files (82+)
b) Update the method that calls stored procedures
4. Regression Testing (Total Effort: 16 hours)

As soon as we got the green light from the CIO to go ahead and make the conversion, our DBA and Lead Developer spent one week-end making the conversion. It surprised me that our actual implementation time was 55 hours, and most of that was spent in data conversion (32 hours).

So on the following Monday, one of developers had a shocking experience. In the morning he was working on one of his features that required saving. Typically, he would open Toad to view the table he was saving to, in order to verify the results. According to him, he was getting pretty mad, because a simple save feature started to look like a nightmare. He would type the values on the form, click save, get no errors, go look for the results in Toad and see no changes in the table, sol he tries to reload the form/restart application/visual studio/computer and see that typed values are loading back, while still not showing in the database. How can you troubleshoot a problem like that?
Luckily, we have "Daily Stand Up Meetings," at which everyone gives updates on items they are currently working and have completed. So as the news of the database switch were announced, you could clearly hear swearing from the developer. Mel, feel free to add to the story.

In the end:
- listening to the boss on why we should be using ORM is 0.0001 man hours,
- choosing an ORM is 40 man hours,
- crash learning NHibernate is 80 man hours,
- getting comfortable with NHibernate is 160 man hours,
- switching database during the development without developers noticing is PRICELESS!


Anonymous said...

Do you have any suggestions for crash learning NHibernate?

Alper said...

When I was learning NHibernate there were not that many examples, so what we did is took an exisiting simple project and re-wrote the persistence layer for the NHibernate. We had to do a lot of trial and error choices, that you can avoid by reading a best practices and feedback.
I recomend to start with reading the documentation. It has been updated and contains a lot valiable information.
check out: dave's blog and .Net Rocks! interview with Oren Eini


Jim Geurts said...

Alper, the cuyahoga project ( is a good example of what can be done w/ nHibernate.

Mel Grubb said...

In the words of MythBusters' Adam Savage... "Well THERE'S your problem".

I don't remember swearing, though. At least not at work.

I would have to say that while many ORMs claim that they isolate you from the database enough that you could totally swap out the back end, this is the first time I've ever seen any project actually DO it. Generally I find that the strength of ORMs or other database abstraction layers help developers the most by allowing you to write code against multiple databases in the same way so that you no longer have to concern yourself with what the back end IS. This is especially helpful for those working on multiple projects at the same time.