NNDB 0.1

I’ve managed to get NNDB, my C++ data storage library which is almost, but not entirely unlike SQL, into a fit state for a release.

You can create tables, set indices on columns, insert data, retrieve data using something like a SELECT, filter it using something like WHERE (which uses indices where available), and order it using something like an ORDER BY.

So far it has been a fantastic way to get my hands dirty with some Template metaprogramming, and some C++ as it should be*, but the reason why I started this was to help me think about how databases work, so I’m really looking forward to getting into how to implement JOINs. At the moment I have only very vague ideas.

NNDB is based heavily on the STL (part of C++’s standard library), BOOST (a playground for things that might one day be in C++’s standard library, and hang-out for some of the cleverest people alive), and Loki (the continuation of Andrei Alexandrescu’s Template metaprogramming (but used for good, not evil?) library written for and explained in Modern C++ Design. This book ranks in the top 5 most exciting books I have read). I continue to be more impressed by all three the more I learn.

I have even been having discussions with the Loki devs about some code I needed for NNDB that I think might be helpful for other people using Loki. It’s called ForEachType and it allows you to loop (at runtime) through all the types in a Typelist and do something for each one.

The project is already working in terms of helping me think about databases. For example, I really hadn’t thought before about how expensive ORDER BY is. To implement it I needed to create a temporary std::map covering the entire result set – in a real database this obviously requires reading every single row before we can even begin to return any results. The way to avoid this is to have an index. Which reminds me: the next thing I need to do is make ORDER BY able to use indices (at the moment it’s only WHEREs that take advantage of them).

So next on my list are:

  • ORDER By uses indices
  • Non-unique indices (presumably implemented with a std::multimap)
  • Joins

I am still very excited so you may see more releases over the next few months.

[* NNDB so far contains zero (0) calls to new and zero (0) calls to delete. Obviously the code it uses (e.g. std::vector) calls them, but that code manages all the memory for me, and most of it uses custom allocators to make it very fast. I have no idea how fast NNDB is, but maybe it could be quite fast. I am pretty confident it doesn’t contain any memory errors. Famous last words…]

2 thoughts on “NNDB 0.1”

  1. You mention in your article that you need TypelistForEach, which (if I understood correctly), doesn’t exist in Loki yet; did you have a look at Boost.MPL (MetaProgramming Library)? It proposes a huge set of type containers along with several algorithms to operate on them at compile-time, such as transform, sort, fold and so on.

    You could also check out Boost.Fusion, a library making the link between pure compile-time computations (cf. MPL) and pure runtime computations (cf. STL). It contains several heterogeneous containers that can be manipulated either at compile-time with metafunctions or at runtime with “classic” functions.

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