In MongoDB how to use $lookup to get not matched records only?
Use one more $match condition at the end of the pipeline
db.master_product_details.aggregate([ { "$match": { "seller_user_id": "seller_id" }}, { "$lookup": { "from": "master_order_details", "localField": "seller_sku_id", "foreignField": "sku_id", "as": "Orders" }}, { "$match": { "Orders": [] }}])