mongosh providing output to --eval as valid JSON syntax

I have a DB with an entities collection with a single document. The following mongosh works ok:

$ mongosh mongodb://localhost:27017/ftest --eval 'db.entities.find()' --quiet

[
  {
    _id: { id: 'E1', type: 'E', servicePath: '/' },
    attrNames: [ 'position' ],
    attrs: {
      position: {
        value: { type: 'Point', coordinates: [ '5.5', '-6.6' ] },
        type: 'geo:json',
        creDate: 1702639380.716183,
        modDate: 1702639380.716183,
        mdNames: []
      }
    },
    creDate: 1702639380.716183,
    modDate: 1702639380.716183,
    location: {
      attrName: 'position',
      coords: { type: 'Point', coordinates: [ 5.5, -6.6 ] }
    },
    lastCorrelator: '4e2f7a0e-9b3c-11ee-98d3-080027cd35f1'
  }
]

However, I need a JSON document no the JavaScript representation of it (i.e the above output doesn't directly validate on typical validators).

I have tried with the --json relaxed or --json canonical options, but I get this error:

$ mongosh mongodb://localhost:27017/ftest --eval 'db.entities.find()' --quiet --json relaxed

{
  "message": "Converting circular structure to EJSON:\n    (root) -> _mongo -> __serviceProvider -> mongoClient -> s -> sessionPool -> client\n                                                  \\-------------------------------/",
  "stack": "BSONError: Converting circular structure to EJSON:\n    (root) -> _mongo -> __serviceProvider -> mongoClient -> s -> sessionPool -> client\n                                                  \\-------------------------------/\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:983314)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at Object.yt [as stringify] (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:986405)\n    at t.formatForJSONOutput (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:53732)\n    at CliRepl.loadCommandLineFilesAndEval (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:32114)\n    at async CliRepl.start (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:29909)\n    at async w (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:80067)",
  "name": "BSONError"
}

$ mongosh mongodb://localhost:27017/ftest --eval 'db.entities.find()' --quiet --json canonical

{
  "message": "Converting circular structure to EJSON:\n    (root) -> _mongo -> __serviceProvider -> mongoClient -> s -> sessionPool -> client\n                                                  \\-------------------------------/",
  "stack": "BSONError: Converting circular structure to EJSON:\n    (root) -> _mongo -> __serviceProvider -> mongoClient -> s -> sessionPool -> client\n                                                  \\-------------------------------/\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:983314)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at /tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:984642\n    at ft (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:985421)\n    at Object.yt [as stringify] (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:1960:986405)\n    at t.formatForJSONOutput (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:53732)\n    at CliRepl.loadCommandLineFilesAndEval (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:32114)\n    at async CliRepl.start (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:29909)\n    at async w (/tmp/m/boxednode/mongosh/node-v20.9.0/out/Release/node:10:80067)",
  "name": "BSONError"
}

As far as I understand my document (see it above) doesn't have any circular dependency... so I don't understand why I'm getting these errors.

So:

Why this error is happening in relaxed and canonical modes?
Is there some way that mongosh provides output as actual JSON instead of JavaScript objects/arrays?

Thanks in advance!

Solution

You can use JSON.stringify(). This should print desired output:

mongosh mongodb://localhost:27017/ftest --eval 'JSON.stringify(db.entities.find().toArray(), null, " ")' --quiet

Note, if you use findOne(), then toArray() is not needed.

If you want to export a collection or part of a collection into JSON, then you can also use mongoexport tool.