How can I execute code stored in a database?

Question

How can I store, for example, the body of a method in a database and later run it? (I'm using Delphi XE2; maybe RTTI would help.)

Answer 1

RTTI is not a full language interpreter. Delphi is a compiled language. You write it, compile it, and distribute only your binaries. Unless you're Embarcadero, you don't have rights to distribute DCC32 (the command line compiler).

However, the JVCL includes a delphi-like language subset wrapped up in a very easy to use Component, called "JvInterpreter". You could write some code (as pascal) and place it in a database. You could then "run that code" (interpreted, not compiled) that you pull from the database. Typically these should be procedures that call methods in your code. YOu have to write some "wrappers" that expose the compiled APIs that you wish to expose to the interpreter (provide access to live data, or database connection objects, or table/query objects). You're thinking that this sounds perfect right? Well, it's a trap.

Beware of something called "the configuration complexity clock". YOu've just reached 9 o'clock, and that's where a lot of pain and suffering begins. Just like when you have a problem, and you solve it with regular expressions, and "now you have two problems", adding scripting and DSLs to your app has a way of solving one problem and creating several others.

While I think the "DLL stored in a database blob field" idea is evil, and absurd, I think that wanton addition of scripting and domain-specific languages to applications is also asking for a lot of pain. Ask yourself first if some other simpler solution could work. Then apply the YAGNI principle (You Ain't Gonna Need It) and KISS (keep-it-simple-smartguy).

Think twice before you implement anything like what you're asking about doing in your question.

Answer 2

Your best Option, IMHO, is using a scripting engine and storing scripts in the database.

Alternatively you could put the code in a dll and put that dll in the database. There is code for loading a dll from a resource into ram and processing it so it can be used as if it was loaded using LoadLibrary, e.g. in dzlib. I don't really know whether works with any dll and in which versions of Windows, but it does with the ones I tried.