[syslog-ng] Dynamic collection name in MongoDb

Hi, I am retrieving the value for *$M_ADDRESS* from the Syslog message using patterndb. $M_ADDRESS is a unique value. Based on that I have to create the collection in MongoDB dynamically. If I provide the value like below it is not recognizing collection("$M_ADDRESS") Is there any alternate way to create it? Please advise. Regards, PCLP.