MongoDB: how to count number of keys in a document?

Question

Lets say a document is :

{

a: 1,
b: 1,
c: 2,
 ....
z: 2
}

How can I count the number of keys in such document?

Thank you

Answer 1

If You are work with Documents like the mongoose.Document, You can try to count all keys inside the doc after transform in a object, 'cause, before it, the doc just have commom properties:

Object.keys(document); // returns [ '$__', 'isNew', 'errors', '_doc', '$locals' ]
Object.keys(document).length; // returns ALWAYS 5

So, try cast to an object, after pass it to Object.keys

console.dir(
    Object.keys(document.toObject()) // Returns ['prop1', 'prop2', 'prop3']
);

And to show the keys count

console.log(
    Object.keys(document.toObject().length)
); // Returns 3

And Be Happy!!!