j-coll

function migrateCollectionDifferentCollection(inputCollection, outputCollection, query, projection, migrateFunc) {
    var bulk = db.getCollection(outputCollection).initializeOrderedBulkOp();
    var count = 0;
    var bulkSize = 500;
    db.getCollection(inputCollection).find(query,projection).forEach(function(doc) {
        migrateFunc(bulk, doc);
        if ( bulk.nUpdateOps + bulk.nInsertOps + bulk.nRemoveOps >= bulkSize ) {
            count += bulk.nUpdateOps + bulk.nInsertOps + bulk.nRemoveOps;
            print("Execute bulk! " + count);
            bulk.execute();