Getting array length in mongodb?

Question

{
  "_id" : 654321,
  "first_name" : "John",
  "last_name" : "Doe",
  "interested_by" : [ "electronics", "sports", "music" ],
  "address" : {
    "name" : "John Doe",
    "company" : "Resultri",
    "street" : "1015 Mapple Street",
    "city" : "San Francisco",
    "state" : "CA",
    "zip_code" : 94105
  }
}

How can i find the name of elements in array 'intersted_by' using command??

Answer 1

您可以通过执行以下操作来计算密钥数量：

var count = Object.keys(myObject).length;

Answer 2

You can have the size of your result in the mongo shell using :

db.collection.count()

Replace collection by the name of your collection. You can also add a find condition like this :

db.collection.find().count()

Like that, you wan restrict your result with deffernts clauses before count the numbers of data corresponding

Edit : don't forget to do the command use databaseName if you're not in your database, it does'nt work