Circles and Crosses

Creating an Object-Relational Mapping (ORM) has become the de facto way of handling persistence in the object-oriented programming paradigm. Almost all systems require some form of persistent state, and relational databases have become the de facto place to put that state. Relational databases are proven, scale well, and organize data in a tabular manner suitable for many of the real world problems that we try to solve, so they are an obvious choice. Choosing them, however, means we have a new problem at our hands, known as the object-relational impedance mismatch.

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I’ve spent the last few days at work implementing a cache in the data access layer (DAL) of one of our services. The cache works great, and speeds up our service very much in some cases, and somewhat in all cases. I’ve implemented caches before, and experienced many of the difficulties that arise when introducing a cache. It always seems rather easy, and always has unwanted side effects. The general advice is of course not to do it (and the advice from the database guys are always not to do it), but here are my five best advices on what you should consider if you decide to do it.

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