The title is not meant to start a war over the concept of ORM. I appreciate the effort that has gone into mappers. But lets take a look at why I hate ORMs. (Dont hate me because I hate ORM :) )
I am beginning to wonder how many applications that we build really need a relational database.
Some terms become synonymous with their usage. For instance in the Xerox has become synonymous with Copiers.
Relational databases have almost become synonymous with Databases. As a developer or anyone involved in system design it is very important to know the options that are available to store data. The choice of persistence technology governs application scaling and performance in a very big way.
Now, Why do I hate ORM
ORMs hide the inconvenience that comes with using RDBMS with object oriented code.
When I learned relational modeling, I really liked it. I still do like making relational models. But how long have relational databases been in existence. They were in existence much before the widespread usage of object oriented programming. Back then code was procedural. The relationship between data had to exist somewhere and it made sense to have it in the persistent store. Querying became easier.
But it was rather hard to switch older persistent stores with other technologies when we moved to object oriented code. Reasons were many. For example: availability skilled database developers, strong trust in RDBMS, good vendor support etc. But the move towards newer languages like C++, java and C# was inevitable. ORMs was win win solution to this problem.
Before ORM, all of us were known to writing a mapping layer ourselves. ORM was such a relief when it hit the markets. It set us free after years of wrangling with ugly mappers. But in the revelry we seem to have forgotten that it was database that needed a second look and not the codebase.
Now we have Duplication of relationships in data as well as in code. It is surprising that duplication of relationships has not struck us as problem.
Even frameworks like rails give us an impression that the standard way to build a web application is to use an RDBMS as a backend.
I simply cannot grasp the amount of effort we put into mapping object to schema. Another annoying issue is to have completed Database Design before starting development. Using Hibernate or Active Record on top of an existing schema is nothing less than tying oneself up in knots.
There is no point in great Object Oriented code if the system design is not appropriate. It is my humble thought that ORM should not be used as an excuse to choose Relational Databases over other options. As in any case use with Discretion.
Let me know what you think.