Question

I’m going to create a schema like this:

[
    {
        username: "fabio",
        password: "xxx",
        roles: [
            {
                rolename: "administrator",
                isVip: true
            },
            {
                rolename: "manager",
                isVip: true
            }
        ]
    },
    {
        username: "marco",
        password: "yyy",
        roles: [
            {
                rolename: "manager",
                isVip: true
            }
        ]
    },
    {
        username: "pippo",
        password: "...",
        roles: [
            {
                rolename: "monkey",
                isVip: false
            }
        ]
    }
]

Now I want to list all roles available in my app, starting from the users collection.

I think about a SELECT DISTINCT rolename FROM ... SQL statement.

I’d like to get a result like {"administrator","manager","monkey"} .

1. Is it possible?

2. What query may I execute? I tought about:

   db.users.find({ “roles.rolename”: { $exists : true }});

   But that will find all users, not all roles.

3. Is it good? Or is it better creating another collection “roles” and keep an array of ObjectIds?

4. I am using Mongoose (mongodb for nodejs) so my query has to be ready for that.

Answer 1

You can use the distinct() command to find the unique values:

> db.users.distinct('roles.rolename')
[ "administrator", "manager", "monkey" ]