How to get from n to n items in mongodb - mongodb

Question

I'm trying to create an android app which pulls first 1-10 documents in the mongodb collection and show those item in a list, then later when the list reaches the end i want to pull 11-20 documents in the mongodb collection and it goes on.
def get_all_tips(from_item, max_items):
db = client.MongoTip
tips_list = db.tips.find().sort([['_id', -1]]).limit(max_items).skip(from_item)
if tips_list.count() > 0:
from bson import json_util
return json_util.dumps(tips_list, default=json_util.default), response_ok
else:
return "Please move along nothing to see here", response_invalid
pass
But the above code does not work the way i intended but rather it returns from from_item to max_items
Example: calling get_all_tips(3,4)
It returns:
Document 3, Document 4, Document 5, Document 6
I'm expecting:
Document 3, Document 4

Answer 1

In your code you are specifying two parameters.
from_item: which is the starting index of the documents to return
max_items: number of items to return
Therefore calling get_all_tips(3,4) will return 4 documents starting from document 3 which is exactly what's happening.
Proposed fixes:
If you want it to return documents 3 and 4 call get_all_tips(3,2) instead, which means return a maximum of two documents starting from 3.
If you'd rather like to specify the start and end indexes in your function, I recommend the following changes:
def get_all_tips(from_item, to_item):
if to_item < from_item:
return "to_item must be greater than from item", bad_request
db = client.MongoTip
tips_list = db.tips.find().sort([['_id', -1]]).limit(to_item - from_item).skip(from_item)
That being said, I'd like to point out that MongoDb documentation does not recommend use of skip for pagination for large collections.
MongoDb 3.2 cursor.skip