nodejs mongodb executeDbcommand error

I am trying to run a text search query on mongodb by using the executeDbcommand method. However, I get the "Object has no method executeDbcommand" error. Here is the code:

var db  = require('mongodb').Db;

db.connect("mongodb://localhost:27017/test",function(error,client){ 

client.executeDbcommand({text: 'Data', search:{'date': { '$gt' : last },"post": rgxp} },      function(e,o){

if(e) { console.log('error:') ; console.log(e); }

else

console.log(o);