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db.collection.aggregate([{$project:{items:{"$map":{"input":"$items","in":{products:{"$filter":{"input":"$$this.products","as":"product","cond":{"$and":[{$ne:["$$product._id.productId",null],},{$ne:["$$product._id.productId",undefined],}]}}}}}}}},{"$match":{"items.products":{$ne:[]}}}])