Ruby code to remove from Mongo

Question

I am wanting to write some ruby to iterate through documents in a collection in a MongoDB.

My data has the schema:

"_id" : ObjectId("560ff830eeb4db07875b59b9"), 
"userId" : NumberInt(1), 
"movieId" : NumberInt(50), 
"rating" : 4.0, 
"timestamp" : NumberInt(1329753504)

I firstly want to count each time userId = 1 is present in the whole collection, and if less than 5 discard them all.

I'm really unsure how to tackle this, so any advice would be great.

Answer 1

You would need to count the number of documents which have userId = 1 through the count() method. Thus from the shell (command-line), you can do the following:

var count = db.collection.find({ "userId": 1 }).count();
if (count < 5) db.collection.remove() 

You'll then have to do something similar with Ruby, but it should be pretty straightforward. Refer to the documentation on the Ruby driver for this:

1. Get a count of matching documents in the collection.
2. Remove documents from the collection