从父节点读取特定叶/子节点的 Firebase 规则

Question

我的 firebase 数据库看起来像这样

"students" : {
  "firebase_key_1" : {
    "Name" : "blah blah",
    "Address" : "blah blah",
    "Roll No" : "blah blah",
    "Marks" : {
        "Sub1" : "blah",
        "Sub2" : "blah",
        "Sub3" : "blah",
        "Total" : "Total",
    },
    "class" : "blah blah",
    "Transportation" : "blah blah",
    "Department" : "blah blah",
},
  "firebase_key_2" : {
    "Name" : "blah blah",
    "Address" : "blah blah",
    "Roll No" : "blah blah",
    "Marks" : {
        "Sub1" : "blah",
        "Sub2" : "blah",
        "Sub3" : "blah",
        "Total" : "Total",
    },
    "class" : "blah blah",
    "Transportation" : "blah blah",
    "Department" : "blah blah",
},
  "firebase_key_3" : {
    "Name" : "blah blah",
    "Address" : "blah blah",
    "Roll No" : "blah blah",
    "Marks" : {
        "Sub1" : "blah",
        "Sub2" : "blah",
        "Sub3" : "blah",
        "Total" : "Total",
    },
    "class" : "blah blah",
    "Transportation" : "blah blah",
    "Department" : "blah blah",
}
}

我正在使用 rest api 从 firebase 检索数据。 Restapi 网址看起来像 https://domain.firebaseio.com/students.json?orderby="Marks/Total"&startAt=400

我已经通过 firebase 规则为学生总数编制了索引。我得到了 Result 以及额外的数据，例如姓名、班级、卷号。

我希望输出是

    "firebase_key_1" : {
    "Marks" : {
        "Sub1" : "blah",
        "Sub2" : "blah",
        "Sub3" : "blah",
        "Total" : "Total",
    }
},
"firebase_key_2" : {
    "Marks" : {
        "Sub1" : "blah",
        "Sub2" : "blah",
        "Sub3" : "blah",
        "Total" : "Total",
    }
},
"firebase_key_3" : {
    "Marks" : {
        "Sub1" : "blah",
        "Sub2" : "blah",
        "Sub3" : "blah",
        "Total" : "Total",
    }
}

有没有办法通过 RestAPi 或规则来做到这一点。

是否有任何规则可以定义例如要读取的节点

{
 "users":{
   "students":{
      ".read" : ["$firebaseKey/Marks"],
      ".write" : true,
   }
   }

这样我就可以使用 Rest api 从父节点检索所需的值。

任何其他这样做的建议都会很棒。

提前致谢

Answer 1

Firebase 数据库始终返回完整的节点。无法获得与您的查询匹配的每个节点的子集。要么返回整个节点，要么不返回。

通常这种类型的请求表明您已经合并了应该分开的多种类型的数据。在您的情况下，您应该有两个顶级集合：students 和 studentMarks。在students 下，您可以保留每个学生的属性，并以学生 ID 为关键字。在studentMarks 下，您可以保留每个学生的分数，再次以学生 ID 为关键字。

所以：

"students" : {
  "firebase_key_1" : {
    "Name" : "blah blah",
    "Address" : "blah blah",
    "Roll No" : "blah blah",
    "class" : "blah blah",
    "Transportation" : "blah blah",
    "Department" : "blah blah",
  },
  "firebase_key_2" : {
    "Name" : "blah blah",
    "Address" : "blah blah",
    "Roll No" : "blah blah",
    "class" : "blah blah",
    "Transportation" : "blah blah",
    "Department" : "blah blah",
  },
  "firebase_key_3" : {
    "Name" : "blah blah",
    "Address" : "blah blah",
    "Roll No" : "blah blah",
    "class" : "blah blah",
    "Transportation" : "blah blah",
    "Department" : "blah blah",
  }
},
"studentMarks": 
  "firebase_key_1" : {
    "Sub1" : "blah",
    "Sub2" : "blah",
    "Sub3" : "blah",
    "Total" : "Total",
  },
  "firebase_key_2" : {
    "Sub1" : "blah",
    "Sub2" : "blah",
    "Sub3" : "blah",
    "Total" : "Total",
  },
  "firebase_key_3" : {
    "Sub1" : "blah",
    "Sub2" : "blah",
    "Sub3" : "blah",
    "Total" : "Total",
  }
}

由于您在 students 和 studentMarks 之间使用相同的密钥，因此您可以轻松地为用户准备两组数据。但是现在您也可以只读取每个用户的属性，或者只读取一组用户的标记。