Almost every serious programming language has to deal with database access, if not out of love, then at least out of practical necessity.

The theoretical background of a functional programming language is somewhat hostile to this, because pure functional langauges tend to dislike state and a database has the exact purpose to preserve state for a long time. Treating the database as somewhat external and describing its access with monads will at least please theoretical purists to some extent.

In case of Scala things are not so strict, it is allowed to leave the purely functional path where adequate. But there are reasons to follow it and to leave it only in well defined, well known, well understood and well contained exceptions… So the database itself may be acceptable.

Another intellectual and practical challenge is the fact that modern Scala architectures like to be reactive, like to uncouple things, become asynchronous. This is possible with databases, but it is very unusual for database drivers to support this. And it is actually quite contrary to the philosophy of database transactions. It can be addressed with future database drivers, but I do not expect this to be easy to use properly in conjunction with transactions.

It is worthwhile to think about
immutability and databases.
For now we can assume that the database is there and can be used.

So the question is, why not integrate existing and established persistence frameworks like JPA, Hibernate, Eclipslink and other OR-mapping-based systems into Scala, with Scala language binding?

Actually I am quite happy they did not go this path. Hibernate is broken and buggy, but the generic concept behind it is broken in my opinion. I do not think that it is theoretically correct, especially if we should program with waterproof transactions and actually defeat them by JPA-caching without even being aware of it? But for practical purposes, I actually doubt that taming JPA for non trivial applications is really easier than good old JDBC.

Anyway, Scala took the approach of building something in the lines of JDBC, but making it nicer. It is called Slick, currently Slick 3. Some links:
* Slick
* Slick 3.1.1
* Documentation
* Github
* Assynchronous DB access
* Recording of the Slick Workshop at ScalaX

What Slick basically does is building queries using Scala language. It does pack the results into Scala structures. Important is, that the DB is not hidden. So we just do the same as with JDBC, but in a more advanced way.

This article is inspired by my visit to Scala X.

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Ein Gedanke zu „Slick

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