Javascript：需要帮助了解 mongooseODM 的异步/等待

Question

const deleteTaskCount = async(id) => {
const task = Task.findByIdAndDelete(id);
const count = await Task.countDocument({completed:false})
return count;

}

deleteTaskCount("1234").then((count)=>{
console.log(count);
})

I understood that with await in const task = Task.findByIdAndDelete(id);it deletes the user with the id.But without the await keyword(like in the above function) the function still happens, that is it deletes the user but in a non-blocking way after some time.When i ran the above code the count is showing properly but the const task = Task.findByIdAndDelete(id); is not deleting the user.

Answer 1

You should use await for the Task.findByIdAndDelete(id) as well. When you use await , NodeJS will go do some other things until that resolves, and it will only then continue to execute the function (it will not block your code at all).

const deleteTaskCount = async(id) => {
  const task = await Task.findByIdAndDelete(id);
  const count = await Task.countDocument({completed:false})
  return count;
}

deleteTaskCount("1234").then((count)=>{
  console.log(count);
})

Answer 2

I don't know much about the mongoose API but I suspect mongoose.query behaves similar to mongo cursors and many other asynchronous database drivers/ORMs. Queries often don't execute unless awaited or chained upon.

In any case, without awaiting Task.findByIdAndDelete , there's no guarantee in concurrency between the two queries. If you want the result of countDocument to reflect the changes in findByIdAndDelete , you must wait on the client-side for that query to complete and then run countDocument .

You would achieve this by adding the await keyword before Task.findByIdAndDelete .

I'd presonally recommend using the promises/thenables as opposed to await/async .

Task.findByIdAndDelete("1234")
  .then(task => Task.countDocument({completed:false}))
  .then(count => console.log(count));

Imho, it's cleaner, less error prone, more functional, less confusing. YMMV