Question

I have a set like so

{date: 20120101}
{date: 20120103}
{date: 20120104}
{date: 20120005}
{date: 20120105}

How do I save a subset of those documents with the date ‘20120105’ to another collection?

i.e db.subset.save(db.full_set.find({date: "20120105"}));

Answer 1

Here’s the shell version:

db.full_set.find({date:"20120105"}).forEach(function(doc){
   db.subset.insert(doc);
});

Note: As of MongoDB 2.6, the aggregation framework makes it possible to do this faster; see melan’s answer for details.