When to Add an ORM Tool

I’m working on the code that parses VCalendar data so that it can be processed. Im copying the data I care about into a simple data structure that can represent a calendar request in any format. Any logic that interacts with calendar requests would use this internal structure. I want it to be simple, only having the stuff that I need, but I don’t want to completely re-invent the wheel either, so I will use the VCalendar format as a guideline.

Ive used this pattern of processing an established or complex data format into a simple proprietary one before with good results. It allows you to isolate the complexities of a data format in the code that processes it, keeping the rest of your code clean. Like everything, there are cases where I wouldn’t use it, but for this kind of scenario it should work well.

Now that I’m building this neutral representation, my next thought is how it will be saved to the database. I don’t need a database at this stage of the project, so part of me wants to ignore the decision until later, but the whole point of the system is to persist and interact with these types, so it’s important that I get it right. If I make simple POCO classes now, and start writing a bunch of code that uses them, I might have to change a lot of code later if I want to switch to types generated by Entity Framework. I could write my own custom code to read and write my own types from the database, then I can use any type I want without restrictions, but it would be a waste to write this plumbing code myself when an ORM can do it faster and better.

Creating a table design now wouldn’t be a simple matter either. I don’t know enough about the needs of the scheduling service to know which parts of the VCalendar format to bring over. If I try to guess now I know I’ll bring over a bunch of stuff that I don’t need, but starting with a simple table and adding fields every time I need one is no fun either. Adding a database to a system is like attaching a ball and chain, and I want to wait until I can be sure I have my model correct before I do it.

It’s need to make a decision, so here it is: I’m going to keep building my own types, and try to keep them. When it comes time to hook up a database, I’ll play around with the new POCO support in Entity Framework 4, and if that fails I’ll try another ORM tool. I may need to change my model a bit to suit the ORM, but Im hoping that it wont need to change much.