the instruction db.model.distinct on the mongodb command line ("deptId"). Length can be implemented, but it can"t be used in node. How do you use it in node?
db.collection("model").aggregate([
{'$group': {_id: "$deptId"}}
]).then((err, c) => {
...
}); distinct method under shell is obsolete and is not recommended. It is believed that this method will be removed in a later version. But distinct is essentially group , which is the same in SQL, so just replace it with group .
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