I have one table membership and another is promo codes.

membership table:
 /* 1 */
{
"_id" : ObjectId("5b62e7050b13587e9febb8db"),
"country_id" : "5a093507f1d45633844096ef",
"type" : "Bronze",
"price" : "30",
}
/* 2 */
{
"_id" : ObjectId("5b6961175140b477032291b7"),
"country_id" : "5a093507f1d45633844096ef",
"type" : "Gold",
"price" : "1000",
}....
promo code table :
 {
"_id" : ObjectId("5cfe23fd075be65883f6d921"),
"final_status" : 1,
"membership" : [
ObjectId("5b62e7050b13587e9febb8db"),
ObjectId("5b6961175140b477032291b7"),
ObjectId("5b6961285140b477032291b8"),
ObjectId("5b7567dd5b874856981b53d3"),
ObjectId("5bba1c3794c6761db256edbc")
],
"month" : [
"1",
"3"
]
}
here, the promomcode table has a membership id. I want promo code data with membership join query.get promo code data with membership detail Please help me