indexing - MongoDB best schema for filterable, dynamic attributes?

Question

I have a large collection of users. Each user can have roles. I want to be able to filter users based on which role they have. Is there a performance difference between the following two approaches? I can imagine the second approach is faster and more appropriate for my use case. I also hypothesize the index for the second one would be smaller. Any ideas? Thanks!

Array approach

{
  name: "Paul",
  roles: [
    "system administrator",
    "network administrator",
    "solutions architect"
  ]
}

Attribute approach

{
  name: "Paul",
  roles: {
    system_administrator: true,
    network_administrator: true
    solutions_architect: true
  }
}

question from:https://stackoverflow.com/questions/65928948/mongodb-best-schema-for-filterable-dynamic-attributes

Answer 1

First approach is better, because you can easily add/remove/update items in your roles array using array operators like $push, $pull etc.

Also, indexing the first type is easier, as you'd just index roles field.

For the next option, if you want to specifically index each type of role, you will have to create a lot of indexes.

So my vote will be for first!