[mongo] flat object

// data
{
    "_id" : ObjectId("5f4f03709f80fb9179d5136e"),
    "data1" : 1.0,
    "data2" : 2.0,
    "data3" : 3.0,
    "data4" : 4.0,
    "data5" : 5.0,
    "other" : {
        "data6" : 6.0,
        "data7" : 7.0,
        "data8" : 8.0,
        "data9" : 9.0,
        "data10" : 10.0
    }
}

// way 1: $project
db.getCollection('test').aggregate([
    { $project: {
        _id: 0,
        data1: 1,
        data2: 1,
        data3: 1,
        data4: 1,
        data5: 1,
        data6: '$other.data6',
        data7: '$other.data7',
        data8: '$other.data8',
        data9: '$other.data9',
        data10: '$other.data10',
    }}
])

// way 2: $replaceRoot & $mergeObjects & $unset($project)
db.getCollection('test').aggregate([
    { $replaceRoot: { newRoot: { $mergeObjects: ['$$ROOT', '$other'] } }},
    { $project: { other: 0 } },
])