$documents - query failed: (InvalidNamespace) '$documents' can only be run with {aggregate: 1}

[GithubArray]

When I try to use $documents operator in playground,

db.collection.aggregate([
  {
    "$documents": [
      {
        "test": 123
      }
    ]
  }
])

I get below error:

query failed: (InvalidNamespace) '$documents' can only be run with {aggregate: 1}

Playground to reproduce.

---

Alternatives that I have tried(but also failed):
Removing collection in db.collection.aggregate([...]): will get syntax error like:

Invalid query:

Line 1: Expected '.' instead of '('

Playground

What could be a correct way to use $documents in Mongo Playground?

[feliixx]

Hi @GithubArray,

Thanks for the report. This is happening because $documents is only available when calling db.aggregate() (ie, not running aggregation on a specific collection). This is not supported by the playground yet and might be tricky to implement, so the best solution for now is to remove the $documents stage, put the documents in an other collection, and run the aggregation on this collection.

[GithubArray]

Just to note a workaround, we can select no document by _id: {$exists: false} and then put the $documents stage in an $unionWith pipeline as a workaround in playground.

db.collection.aggregate([
  {
    "$match": {
      _id: {
        "$exists": false
      }
    }
  },
  {
    "$unionWith": {
      "coll": "collection",
      "pipeline": [
        {
          "$documents": [
            {
              "hello": "world"
            }
          ]
        }
      ]
    }
  }
])

Mongo Playground