Firebase 3 auth通过slug？

Question

我试图在我的firebase数据库上实现我的数据库规则。

现在我有：

{
  "rules": {
    ".read": false,
    ".write": false,
    "users": {
      ".read": true,
      ".write": "(auth != null) && !root.child('users/'+ newData.child('slug').val()).exists()",
      "$username": {
        ".read": false,
        ".write": false,
        "clubs": {
          ".read": "(auth != null)",
          ".write": false
        },
        "roles": {
          ".read": "(auth != null)",
          ".write": false
        }
      }
    },
    "clubs": {
      ".read": true,
      ".write": true
    }
  }
}

，数据如下：

{
    clubs: {
        smash_for_fun: {
            description: "The best club ever!",
            name: "Smash For Fun",
            slug: "smash_for_fun",
            users: {
                glenn_lastname: true
            }
        }
    },
    users: {
        glenn_lastname: {
            clubs: {
                smash_for_fun: true
            },
            name: "Glenn Lastname",
            slug: "glenn_lastname",
            uid: "edtJDkUnEOXAUnl0J9GfXIsOqgG2"
        },
        other_user: {
            name: "Other user",
            slug: "other_user",
            uid: "sgsdkjfnsdfnsdkjfnlsdfndsjfn"
        }
    }
}

但我如何制定规则，以便用户只能编写自己的详细信息，而不是来自其他用户呢？

以及如何检查user.slug是否不存在？