I’m currently programming in Scala, but I guess this applies to any functional programming language, or rather, any programming language that recommends immutability and can interact with a database.
When I fetch data from my database, I map it to a model data structure. In functional programming, data structures tend to be immutable. But the data in a database is mutable, so I wonder whether or not my model should be mutable as well. In general, what would be a good and well-accepted practice in such a case?
Following Scala courses by Martin Odersky on Coursera, I remember he said something like:
It’s better to use immutable data structures, but when you want to
interact with the real world, it can be useful to use mutable data
structures.
So, again, I wonder what should I do. As of now, my data structures are immutable, and this is leading to a lot of boilerplate code when I want to update a record in my database. Would using a mutable model help reduce this boiler plate?
(I already asked a similar question which was quite specific to the technologies I use, but I wasn’t satisfied with the actual answers, so I’ve generalized it here.)
“Interacting with the real world” has nothing to do with whether you use mutable or immutable data structures. This is a furfy that is repeated all too often and it is great that you have questioned it.
While it is typically more healthy to dismiss garbage like this, you might be interested in a cursory debunking:
http://blog.higher-order.com/blog/2012/09/13/what-purity-is-and-isnt/
However, I strongly recommend dismissing it and moving on.
Onto your question, you say you have boilerplate when you want to perform operations on your immutable data structures. In fact, there is very well established theory that solves this problem to a large extent. Here is a paper written about it using Scala:
http://dropbox.tmorris.net/media/doc/lenses.pdf
Hope that helps.