MongoDB update object in Array

Question

I have the following document:

{
 "name" : "student_1",
 "courses" : [
 {
 "name" : "Algebra",
 "grades" : [ 98, 96, 92 ]
 },
 {
 "name" : "Computers",
 "grades" : [ 80 ]
 }
 ]
}

How can I update the grades of a specified course? For example, I want to increment some test in the course Algebra by 10 points.

Answer 1

'some test', so let's say you want to add 10 to 96 :

db.student.update({name:'student_1','courses.name':'Algebra'},{$inc:{"courses.$.grades.1":10}})

In the find part, you point to the courses with name 'Algebra'. The .$ points you to that found element. Of that found element, it will change the second (.1) value in the grades array. Using $, you don't need to know the position of the course in the array.

• itaied: The $ gives me the first element, what if I want to update Computers course? Do I have to know the position of the course in the array?
• aldwinaldwin: In the find part, you point to the courses with name 'Algebra'. The .$ points you to that found element. Of that found element, it will change the second (.1) value in the grades array. Using ,ドル you don't need to know the position of the course in the array.