MongoDB 复杂查询 $where 子句

复杂的MongoDB查询，除非万不得已，不然不要用 $where

{ "$or" : { "first_name": "Dany" , "last_name": "Fang" },{ "first_name": "Amber " , "last_name": "Wei" } }
<=> 等價于 
"$where": "function()  {  \
    var key = {'Dany Fang':1,'Amber Wei:1};   \
    var id = this.first_name+' '+ this.last_name; 
    return key[id] ? true : false;   \
 }"