In Mongoose Model.find() and Model.find().exec() produce the same result. So why bother using Model.find().exec()?

Question

I noticed that Model.find() seems to produce the same outcome as Model.find().exec(). Both seem to retrieve the appropriate record/document as illustrated in the following two snippets of code:

//without exec
export const getUser = async (req, res, next) => {
    try{
        let mongoDocument = await User.find({name: "OrphanAnnie"})
        res.status(200).json(mongoDocument);  
    } catch (err) {
        console.log(err) 
    }
}

//with exec
export const getUser = async (req, res, next) => {
    try{
        let mongoDocument = await User.find({name: "OrphanAnnie"}).exec()
        res.status(200).json(mongoDocument);  
    } catch (err) {
        console.log(err) 
    }
}

Which is the recommended approach? In Mongoose - What does the exec function do? the post suggests that with exec() a Mongoose query can be built without using callback syntax. But since the query seems to work without using exec() at all why bother using it?

Only very imperfectly. That post suggests that exec() allows you to execute a Mongoose query without a callback. But it seems like one can execute the Mongoose query even without exec(). — Luke, Apr 04 '21 at 18:10
BTW, one can also execute the query this way: export const getUser = (req, res, next) => { User.find({ name: "OrphanAnnie" }) .then(function (user) { return res.json(user); }) .catch(function (err) { return res.json(err); }); } But even while this works, it doesn't clarify what the exec does when using the await syntax approach.... — Luke, Apr 04 '21 at 18:11

turivishal · Accepted Answer · 2021-04-04T19:21:13.213

Mongoose have explained the difference of both in promises,

There are two alternatives for using await with queries:

await Band.find();

await Band.find().exec();

As far as functionality is concerned, these two are equivalent. However, we recommend using .exec() because that gives you better stack traces.

With the example:

const doc = await Band.find({ name: "Guns N' Roses" }); // works

const badId = 'this is not a valid id';
try {
  await Band.find({ _id: badId });
} catch (err) {
  // Without `exec()`, the stack trace does **not** include the
  // calling code. Below is the stack trace:
  //
  // CastError: Cast to ObjectId failed for value "this is not a valid id" at path "_id" for model "band-promises"
  //   at new CastError (/app/node_modules/mongoose/lib/error/cast.js:29:11)
  //   at model.Query.exec (/app/node_modules/mongoose/lib/query.js:4331:21)
  //   at model.Query.Query.then (/app/node_modules/mongoose/lib/query.js:4423:15)
  //   at process._tickCallback (internal/process/next_tick.js:68:7)
  err.stack;
}

try {
  await Band.find({ _id: badId }).exec();
} catch (err) {
  // With `exec()`, the stack trace includes where in your code you
  // called `exec()`. Below is the stack trace:
  //
  // CastError: Cast to ObjectId failed for value "this is not a valid id" at path "_id" for model "band-promises"
  //   at new CastError (/app/node_modules/mongoose/lib/error/cast.js:29:11)
  //   at model.Query.exec (/app/node_modules/mongoose/lib/query.js:4331:21)
  //   at Context.<anonymous> (/app/test/index.test.js:138:42)
  //   at process._tickCallback (internal/process/next_tick.js:68:7)
  err.stack;
}

Other as well: Queries are not promises:

Mongoose queries are not promises. They have a .then() function for co and async/await as a convenience. If you need a fully-fledged promise, use the .exec() function.

const query = Band.find({name: "Guns N' Roses"});
assert.ok(!(query instanceof Promise));

// A query is not a fully-fledged promise, but it does have a `.then()`.
query.then(function (docs) {
  // use docs
});

// `.exec()` gives you a fully-fledged promise
const promise = query.exec();
assert.ok(promise instanceof Promise);

promise.then(function (docs) {
  // use docs
});

Awesome! This clarifies things. Thank you very much. A big thumbs up to you! And nice sleuthing in the Mongoose docs. If you simply search on "Exec" as i did in the Mongoose search field the page you cite AFAIK does not appear. Is that a problem with the docs? Or are you using some other logic to find that info? — Luke, Apr 04 '21 at 19:23

In Mongoose Model.find() and Model.find().exec() produce the same result. So why bother using Model.find().exec()?

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