❔ MONGO - Aggregate pipeline - GroupBy mutliple fields

[{
  UserId:1,
  Badges: [
    { BadgeId:1, Email: "my.mail@foo.com", ExternalId: 111 },
    { BadgeId:2, Email: "my.mail@foo.com", ExternalId: 222 }
  ]
},
{
  UserId:2,
  Badges: [{
    { BadgeId:3, Email: "my.mail@foo.com", ExternalId: 111 }
  ]
},
{
  UserId:3,
  Badges: [{
    { BadgeId:4, Email: "my.mail@foo.com", ExternalId: 222 }
    { BadgeId:5, Email: "NOPNOP@foo.com", ExternalId: 222 }
  }],
},
{
  UserId:4,
  Badges: [{
    { BadgeId:6, Email: "my.mail@foo.com", ExternalId: 111 }
    { BadgeId:7, Email: "my.mail@foo.com", ExternalId: 111 }
    { BadgeId:8, Email: "NOPNOP@foo.com", ExternalId: 222 }
  }],
}]

db.Foos.aggregate([
  { $unwind: { path: "$Badges" } }
])