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mongodbmongo-shellmongosh
CodeoftheWarrior
CodeoftheWarrior

Reputation: 363

Issue iterating over collections in MongoDB from mongo shell

I am trying to create a script that connects to a MongoDB instance, selects a database, lists all the collections from a database and then creates a schema to use for validation from a sample of documents. The latter half of this I have figured out, but I am completely stumped as to how to do the first part. Here's what I have so far this is file runner.js that I am loading from mongosh by running load("runner.js") in the shell prompt:

async function run() {
    const db = connect('mongodb://localhost/mainDB')

    // const collections = db.runCommand({
    //     listCollections: 1.0,
    //     nameOnly: true
    // });
    const coll = db.listCollections();

    console.log(collections);

    for await (const doc of collections) {
        console.log(doc);
    }
}

run().catch(reason => console.error('ERROR RUNNING: ', reason));

When I run the above, I get the following error: ERROR RUNNING: TypeError: db.listCollections is not a function

Bollocks, the API documentation says it's a method https://mongodb.github.io/node-mongodb-native/6.9/classes/Db.html#listCollections

No matter, though, when I uncomment out the commented section above and use the runCommand method, I get the following error:

{
  cursor: {
    id: Long('0'),
    ns: 'mainDB.$cmd.listCollections',
    firstBatch: [
      { name: 'purchaseOrderLineItems', type: 'collection' },
      { name: 'transactionCost', type: 'collection' },
      { name: 'addresses', type: 'collection' },
      ...<more I am not listing here>
    ]
  },
  ok: 1
}
ERROR RUNNING:  TypeError: collections is not async iterable

This also doesn't make sense. Documentation here https://www.mongodb.com/docs/drivers/node/current/fundamentals/crud/read-operations/cursor/ says that the cursor, (which this is, right) implements the async iterable interface, so this should work.

Would someone clarify what is going on here?

Upvotes: 0

Views: 36

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