[odb-users] Dynamic Database usage for scripting?

Boris Kolpackov boris at codesynthesis.com
Mon Sep 9 13:32:12 EDT 2013

Hi Rafal,

Rafal Gm <grasmanek94 at gmail.com> writes:

> I would like to bind a scripting language to my application and somehow
> expose the ODB features.

I think it is useful to distinguish between these two cases:

1. Exposing an ODB-persistent C++ class(es) to a scripting language. This
   should be fairly straightforward since, in a nutshell, all ODB does is
   add database persistence support to a plain C++ class. Though, admittedly,
   things get trickier if you also want to be able to construct and run
   arbitrary queries from a scripting language (native queries are probably
   the best option here).

2. Expose the ODB functionality itself to a scripting language. That is,
   allow "classes" as defined in a scripting language to be persisted via
   ODB. This will be a lot harder and it is probably a better idea to use
   an ORM designed for that scripting language specifically.

It seems to me you are after some variant of #2.

> How would I design a class that at the same time works with odb and can be
> used to provide enough dynamic-ality (sorry bad english) for a scripting
> language? What's compiled is compiled and can't be changed. and a script
> can always be reloaded, For example the script could use it's own colums
> which are not in the C++ compiled code.

Well, just one idea: instead of having normal data members, your class
data could be defined as a set of name-value pairs:

#pragma db object
class dynamic_object
  std::map<std::string, std::string> data;

Then the script can do all sorts of "dynamic" things with the data (e.g.,
add new "columns", discover existing ones, etc).


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