db.collection(collection).find(<query>) returns empty array as soon as query object contains properties

Question

I'm writing my own CLI, which performs some actions against a MongoDB database using mongoose.

Everything works except for the fact that as soon as the query object is something other than {}, I get no results despite documents existing. See below for an example.

const program = require('commander');
const mongoose = require('mongoose');
const jsonParser = require('../helpers/json-parser');

program
  .command('get <collection>')
  .option('-q,--query <query>', 'MongoDB query object', jsonParser)
  .option('-qo,--query-options [query-options]', 'MongoDB query options object', jsonParser)
  .description('Returns documents from a MongoDB collection')
  .action(action);

program.parse(process.argv);

function action(collection, options) {

  let db;

  mongoose.connect('<my-mongo-url>', { useNewUrlParser: true }).then(() => {

    db = mongoose.connection.db;

    console.log(options.query);
    return db.collection(collection).find(options.query, options.queryOptions).toArray().then((docs) => {
      console.log(docs);
      mongoose.disconnect();
    });
  })
  .catch((err) => {

    if (db) {
      mongoose.disconnect();
    }
  });
}

Running $ my-cli get users -q '{}' gives the following result:

[ { _id: 5cfe593b3bb7cb82644651f0, email: '[email protected]', createdAt: 2019-06-10T13:20:59.784Z, updatedAt: 2019-06-10T13:20:59.784Z, role: 'user', __v: 0 } ]

Running $ my-cli get users -q '{"_id": "5cfe593b3bb7cb82644651f0"}' gives the following result:

[]

Running $ my-cli get users -q '{"limit": 1}' gives the following result:

[]

Running $ my-cli get users -q '{"skip": 0}' gives the following result:

[]

I even tried doing db.collection(collection).find({_id: "5cfe593b3bb7cb82644651f0"}) directly in the code but it still only gives me an empty array.

I expect all of these queries to output the same thing but they don't. Why is this?

L_K · Accepted Answer · 2019-06-13 07:18:22Z

1

The _id in mongoDB is not string, actually it's an instance of ObjectId. So maybe you should go db.collection(collection).find({_id: ObjectId("5cfe593b3bb7cb82644651f0")}).

As for '{"limit": 1}' and '{"skip": 0}', I understand that you want to Modify the Cursor Behavior to limit or skip the search results.

However, the db.collection.find receive two params: query and projection, so passing '{"limit": 1}' or '{"skip": 0}' as the find secondary param maybe not what you want.

edited Jun 13, 2019 at 7:18

answered Jun 12, 2019 at 9:17

L_K

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Comments

virgiliogm · Accepted Answer · 2019-06-12 09:07:30Z

1

You are using Mongoose but not using Schemas and querying directly to MongoDB (so I don't understand the purpose of using it.). This way, you should compare the _id field with an ObjectId:

db.collection(collection).find({_id: ObjectId("5cfe593b3bb7cb82644651f0")})

or

$ my-cli get users -q '{"_id": ObjectId("5cfe593b3bb7cb82644651f0")}'

If I'm not wrong, the other queries are not running because you are passing options as query filters and you should use the -qo flag:

$ `my-cli get users -qo '{"limit": 1}'

answered Jun 12, 2019 at 9:07

virgiliogm

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