नेवला ने वादों<में दोनों के अंतर को समझाया है /ए> ,
उदाहरण के साथ:
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;
}
अन्य भी:प्रश्न वादे नहीं हैं :
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
});