Looks as you mix up here several things. This thread here is about ispconfig 2 (its in the ispconfig 2 forum) and ispconfig 2 does not has a function processDatalog. ISPConfig 3 has this function, but thats a completely different software that works differently.
So which ispconfig version do you use?
I've made some simple changes in ISPConfig's source (changes in web_domain db schema - added field, vhost template changed.....) and I'm affraid that it's not gonna work without messing with API's source too (maybe I'm wrong).
I hope you are aware that you are not able to install any ptches or updates for ispconfig anymore as the updater will remove your complete databse on the next update if your databae scheme is different to the one from ispconfig. So adding any fields is a bad idea if you want to benefit from new features in future ispconfig versions.