CODEWITHSUNDEEP
node.jsmongodb
MrSimonEmms
MrSimonEmms

Reputation: 1481

Can I execute a raw MongoDB query in node-mongodb-native driver?

FYI - I know how to use the MongoDB driver and know this is not how one would use it in a web app, but this is not for a web app. My aim is to emulate the MongoDB shell in NodeJS

I'm writing a DB GUI and would like to execute a raw MongoDB query, eg db.tableName.find({ col: 'value' }). Can I achieve this using the native MongoDB driver? I'm using v2.2, which is current the latest version.

If not, how can I achieve this in NodeJS?

Upvotes: 5

Views: 3919

Answers (1)

rsp
rsp

Reputation: 111366

Note: The question has changed - see the updates below.

Original answer:

Yes.

Instead of:

db.tableName.find({ col: 'value' })

You use it as:

db.collection('tableName').find({ col: 'value' }, (err, data) => {
    if (err) {
        // handle error
    } else {
        // you have data here
    }
});

See: http://mongodb.github.io/node-mongodb-native/2.2/api/Collection.html#find

Update

After you changed your question and posted some comments it is more clear what you want to do.

To achieve your goal of emulating the Mongo shell in Node you would need to parse the command typed by the user and execute the appropriate command while keeping in mind:

  1. the difference between SpiderMonkey used by the Mongo shell and Node with V8 and libuv
  2. the difference between BSON and JSON
  3. the fact that Mongo shell works synchronously and the Node driver works asynchronously

The last part will probably be the hardest part for you. Remember that in the Mongo shell this is perfectly legal:

db.test.find()[0].x;

In Node the .find() method doesn't return the value but it either takes a callback or returns a promise. It will be tricky. The db.test.find()[0].x; case may be relatively easy to handle with promises (if you understand the promises well) but this will be harder:

db.test.find({x: db.test.find()[0].x});

and remember that you need to handle arbitrarily nested levels.

The Mongo protocol

After reading some of the comments I think it's worth noting that what you actually send to the Mongo server has nothing to do with the JavaScript that you write in the Mongo shell. The Mongo shell uses SpiderMonkey with a number of predefined functions and objects.

But you don't actually send JavaScript to the Mongo server so you can't send things like db.collection.find(). Rather you send a binary OP_QUERY struct with a collection name encoded as a cstring and a query encoded as BSON plus a bunch of binary flags. See:

The BSON is itself a binary format with a number of low level values defined as bytes:

The bottom line is that you don't send to the Mongo server anything resembling what you enter in the Mongo shell. The Mongo shell parses the things that you type using the SpiderMonkey parser and sends binary requests to the actual Mongo server. The Mongo shell uses JavaScript but you don't communicate with the Mongo server in JavaScript.

Example

Even the JSON query object is not sent to Mongo as JSON. For example, when you are searching for a document with a hello property equal to "world" you would use {hello: 'world'} in JavaScript or {"hello": "world"} in JSON but this is what gets send to the Mongo server - by the Mongo shell or by any other Mongo client:

\x16\x00\x00\x00\x02hello\x00\x06\x00\x00\x00world\x00\x00

Why it's so different

To understand why the syntax used in Node is so different from the Mongo shell, see this answer:

Upvotes: 6

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