How to access the properties of a query result in Mongo - mongodb

Question

I can find a document on my database. A call to:
subject = await Subject.find({ name: 'Math' });
res.send(subject);
returns the document correctly:
{
"topics": [],
"_id": "5ab71fe102863b28e8fd1a3a",
"name": "Math",
"__v": 0
}
The problem is when I try to access the properties of subject. Any of the following calls returns nothing:
res.send(subject._id);
res.send(subject.name);
I've tried subject.toObject() and subject.toArray() but I receive an error:
(node:2068) UnhandledPromiseRejectionWarning: TypeError: subject.toObject is not a function
Any help will be appreciated. Thanks!
NB:
before res.send(subject), I called console.log(subject) and the output is:
[ { topics: [],
_id: 5ab71fe102863b28e8fd1a3a,
name: 'cocei5',
__v: 0 } ]

Answer 1

That is because find method in MongoDB always returns an array.
subject = await Subject.find({ name: 'Math' });
So in above line the Subject.find({name: 'Math'}) is returning an array. Which you are storing in subject variable. if you are getting only single object from DB then you might access the object properties by using subject[0].propertyName.
like if you want to send just an id you can do it by
res.send(subject[0]._id);

Answer 2

You can always use the es6 destructuring feature to get the first element returned in the array, as long as you are sure the result will always be on the 0th index.
const [subject] = await Subject.find({ name: 'Math' });
res.send(subject._id);
res.send(subject.name);
ref: Destructuring arrays and objects
Details for find api
OR you can either use
const subject = await Subject.findOne({ name: 'Math' });
res.send(subject._id);
res.send(subject.name);
As findOne return object whereas find returns an array of objects.
ref: Details for findOne api