I am having graph database which is collection of events and attendees. 

I store `start_time` property of an event as `unix timestamp` so that its easier to search upcoming events just by comparing `unix timestamp`. 

Now the problem is by mistake I stored date string as `start_time` value in few events and now I can not compare date string with `unix timestamp`, and thats why query returns no events. 

How can I compare data type of start\_time property before comparing its value?

Please guide me the correct way to achieve my objective..