Why does `count` perform query collection?

[mingfang]

According there https://softinstigate.atlassian.net/wiki/display/RH/Query+Documents#QueryDocuments-Counting, the count parameter queries the collection, twice. why? The mongodb documentation clearly states that count() does not query at all, https://docs.mongodb.org/v3.0/reference/method/db.collection.count/.

Is there a way to execute the native mongodb version of count()?

[ujibang]

RESTHeart actually performs the count using the "nativa mongodb version of count()"

see public long getCollectionSize(final DBCollection coll, final Deque<String> filters) in CollectionDAO

so, in order to add the collection size to the response, it needs to execute two queries:

• colllection.count(filter) -> this gets the collection _size
• *collection.find(filter).skip(pagepagesize).limit(pagesize)** -> this gets the documents