Is there any better way other than iterating through cursor of MongoDB?

Question

I am doing the following business logic in my code

Cursor cursor = db.getCollection(CollectionInfo.ORDER).aggregate(pipelines, options);
        while (cursor.hasNext()) {
            orders.add(new Order(cursor.next().toMap()));
        }
        return orders;

So just to build the object I am iterating through all the documents. SO If I have a lot of documents as the result of aggregation. The iteration is taking a lot of time. Is there any better way to do this? With Spring data mongo DB or anything else?

Answer 1

Use mongoTemplate.aggregate(...).getMappedResults()

@Autowired
protected MongoTemplate mongoTemplate;
...

List<AggregationOperation> pipeline = ...;
Aggregation agg = Aggregation.newAggregation(pipeline)
    .withOptions(...);
List<Orders> orders = mongoTemplate.aggregate(agg, CollectionInfo.ORDER, Order.class)
    .getMappedResults();

Note: If your query returns more than 1K documents, it's recommended to use $skip / $limit

Pseudocode

skip  = 0
limit = 1_000
size  = 0
do {
   
   //Add skip / limit (do not insert these stages more than once)
   pipeline.add(Aggregation.skip(skip))
   pipeline.add(Aggregation.limit(limit))
   
   //aggregate
   result = mongoTemplate.aggregate(...).getMappedResults();
   
   size  = result.size();
   skip += limit;
// If there are 1_000 results, probably there are more items, keep iterating
} while(size == limit);