MongoDB query to handle/fetch inner array (Need to apply pagination in inner array)

Question

I have a collection with documents like below,

Document1:

{
    name: "tester1",
    reports: [{
            name: "report1",
            type: "overflow"
        },
        {
            name: "report2",
            type: "invalid form"
        }
    ]
}

Document2:

{
    name: "tester2",
    reports: [{
            name: "report3",
            type: "crossed"
        },
        {
            name: "report4",
            type: "unknown issue"
        }
    ]
} 

Document3:
{
    name: "tester3",
    reports: [{
            name: "report4",
            type: "try again"
        },
        {
            name: "report6",
            type: "invalid data"
        }
    ]
}

I am trying to implement query to fetch data like,

[{
        name: "report1",
        type: "overflow"
    },
    {
        name: "report2",
        type: "invalid form"
    },
    {
        name: "report3",
        type: "crossed"
    },
    {
        name: "report4",
        type: "unknown issue"
    },
    {
        name: "report4",
        type: "try again"
    },
    {
        name: "report6",
        type: "invalid data"
    }
]

I tried using grouping and projecting but unable to generate this output.

I need only inner arrays as final documents so that I can apply aggregation queries to achieve pagination and search.

Each document contains above array? I am trying to understand your document — Sohan
– Sohan, Commented Jul 23, 2020 at 11:10

mickl · Accepted Answer · 2020-07-23 13:01:39Z

1

You can use $unwind along with $replaceRoot in order to promote reports to the root level and then you can use $skip or $limit:

db.collection.aggregate([
    { $unwind: "$reports" },
    { $replaceRoot: { newRoot: "$reports" } },
    { $limit: 5 }
])

Mongo Playground

answered Jul 23, 2020 at 13:01

mickl

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