Firebase sample code for question on Stack Overflow

gistfile1.txt

Database:
"root": {
  "reservations": {
    "-59a9ac14cf84dddb10852e65": {
      "details": {
        "message": "in labore velit quis commodo.",
        "children": 0,
        "adults": 5,
        "tel": "+36-96-055-6277",
        "email": "[email protected]",
        "name": "Rivas Knox"
      },
      "public": {
        "handled": false,
        "to": "2017-9-25",
        "from": "2018-12-9",
        "roomId": 2
      }
    }
  }
}

Rules:
"rules": {
  "reservations": {
    "$reservation": {
      "public": {
        ".read": true
      },
      "details": {
        ".read": "root.child('admins').hasChildren([auth.uid])"
      }
    }
  }
}