db.products.aggregate([ {$unwind: "$ratings"}, {$match: {'ratings.user': ObjectId("5f6e2e0b70eb0208fc8401a1")}} ])
db.test.aggregate([ {$match: {'shapes.color': 'red'}}, {$project: { shapes: {$filter: { input: '$shapes', as: 'shape', cond: {$eq: ['$$shape.color', 'red']} }}, _id: 0 }} ])