How to Implement Optimal Pagination in MongoDB?

(Implementing pagination in MongoDB)

Skip-based pagination is not recommended for large datasets due to its memory consumption. An alternative approach for pagination is using natural order by _id field. However, retrieving the last document's _id is a challenge for beginners.

(Forward Paging)**

Forward paging involves iterating through pages in sequential order, storing the _id of the last item on each page.

For natural order such as _id, the process is simple:

1. Find the first page: db.users.find().limit(pageSize).
2. Get the _id of the last document: last_id = ....
3. Find the next page: users = db.users.find({'_id' > last_id}). limit(10);.

(Non-Natural Order)**

For non-natural orders, such as rank, the process becomes more complex:

1. On the first page, store the _ids of retrieved documents and the lastSeen rank:

   • var seenIds = [];, var lastSeen = null;
   • Store _id and update lastSeen while iterating through the cursor.

2. On subsequent pages, exclude seen _ids and retrieve documents with rank less than or equal to lastSeen:

   • db.junk.find( {_id: { $nin: seenIds }, rank: $lte: lastSeen } ).sort({ "rank": -1 }).limit(2);

(Considerations)**

• Maintain a list of seen _ids to exclude results on subsequent pages.
• Store the lastSeen value and discard seen _ids when the rank changes (for non-natural orders).

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