Mongo - Empty object to query string

Question

transporters.count({ '$and': [ {} ] })

transporters.count({ })

Is it the same?

Is it possible the empty object cause speed issues?

kevinadi · Accepted Answer · 2018-03-08 23:33:26Z

1

Yes both queries are considered the same.

This can be seen in the explain output of both queries:

> db.test.explain().count({})
{
  "queryPlanner": {
    "plannerVersion": 1,
    "namespace": "test.test",
    "indexFilterSet": false,
    "winningPlan": {
      "stage": "COUNT"
    },
    "rejectedPlans": [ ]
  },
....

and:

> db.test.explain().count({$and:[{}]})
{
  "queryPlanner": {
    "plannerVersion": 1,
    "namespace": "test.test",
    "indexFilterSet": false,
    "winningPlan": {
      "stage": "COUNT"
    },
    "rejectedPlans": [ ]
  },
....

The explain() output of both queries are identical, meaning both queries will execute the same way.

answered Mar 8, 2018 at 23:33

kevinadi

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