Mongooseでは、Model.find（）とModel.find（）。exec（）は同じ結果を生成します。では、なぜModel.find（）。exec（）をわざわざ使用するのでしょうか。

マングースは、promisesで両方の違いを説明しています 、

例：

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;
}

その他：クエリは約束ではありません ：

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
});