let mut vec = Vec::new(); for n in 0..10000 { let new_doc = doc! { "title": "T", "year": 2020, "plot": "plot description", }; vec.push(new_doc); } all.insert_many(vec, None).unwrap(); // drop collection let pipeline = vec![ doc! { "$documents": [ { "dens": 0 } ] }, doc! { "$densify": { "field": "dens", "range": { "step": 1, "bounds": [0, 10000]} }}, doc! { "$addFields": doc! { "title": "T", "year": 2020, //"rand": {"$rand": {} }, "_id": {"$rand": {} }, }}, // doc! { "$out": "all" }, doc! { "$merge": "all" }, ]; db.aggregate(pipeline, None).unwrap();