How to use MongoDB aggregation for pagination?

Question

I want to perform an aggregation query that does basic pagination:

1. Find all orders that belongs to a certain company_id
2. Sort the orders by

Answer 1

To calculate totals and return a subset, you need to apply grouping and skip/limit to the same dataset. For that you can utilise facets

For example to show 3rd page, 10 documents per page:

db.Order.aggregate([
    { '$match'    : { "company_id" : ObjectId("54c0...") } },
    { '$sort'     : { 'order_number' : -1 } },
    { '$facet'    : {
        metadata: [ { $count: "total" }, { $addFields: { page: NumberInt(3) } } ],
        data: [ { $skip: 20 }, { $limit: 10 } ] // add projection here wish you re-shape the docs
    } }
] )

It will return a single document with 2 fields:

{
    "metadata" : [ 
        {
            "total" : 300,
            "page" : 3
        }
    ],
    "data" : [ 
        {
            ... original document ...
        }, 
        {
            ... another document ...
        }, 
        {
            ... etc up to 10 docs ...
        }
    ]
}