Question

JSON数据显示各种学院中的可用学科：

{
  "AvailableDisciplines": {
    "4JN": {
      "Disciplines": {
        "CV": {
          "disciplineCode": "CV",
          "disciplineName": "Civil Engineering",
          "siNo": "1"
        },
        "EC": {
          "disciplineCode": "EC",
          "disciplineName": "Electronics and Communication Engineering",
          "siNo": "2"
        },
        "EE": {
          "disciplineCode": "EE",
          "disciplineName": "Electronics and Electricals Engineering",
          "siNo": "3"
        }
      }
    },
    "4MT": {
      "Disciplines": {
        "EE": {
          "disciplineCode": "EE",
          "disciplineName": "Electronics and Electricals Engineering",
          "siNo": "1"
        },
        "CS": {
          "disciplineCode": "CS",
          "disciplineName": "Computer Science Engineering",
          "siNo": "2"
        },
        "IS": {
          "disciplineCode": "IS",
          "disciplineName": "Information Science Engineering",
          "siNo": "3"
        }
      }
    },
    "1KT": {
      "Disciplines": {
        "TE": {
          "disciplineCode": "TE",
          "disciplineName": "Telecommunication Engineering",
          "siNo": "1"
        },
        "CS": {
          "disciplineCode": "CS",
          "disciplineName": "Computer Science Engineering",
          "siNo": "2"
        },
        "IS": {
          "disciplineCode": "IS",
          "disciplineName": "Information Science Engineering",
          "siNo": "3"
        }
      }
    }
  }
}

其中4JN，4MT和1KT是学院代码。如果要查询所有提供土木工程学科的学院，则必须在AvailableDisciplines节点上写一个深层查询。查询代码为：

FirebaseDatabase.getInstance().getReference()
    .child("Trial").child("AvailableDisciplines")
    .orderByChild("Disciplines/EE").startAt("")
    .addListenerForSingleValueEvent(new ValueEventListener() {      
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            Log.v("log", "datasnapshot: " + String.valueOf(dataSnapshot));
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
}));

我能够按照我的期望获取数据。但是，在这种情况下，我不知道如何编写.indexOn规则。你能帮我吗？

Answer 1

这是示例规则代码：正如您在下面看到的，密钥有多深无关紧要。

{
  "rules": {
    ".read": true,
    ".write": "auth != null",
    "AvailableDisciplines": {
      "$otherKeys":{
       ".indexOn":["disciplineName"] 
      }
    }
   }
 }

您可以在同一级别添加更多密钥，即：".indexOn":["disciplineName", "disciplineCode","siNo"]

Answer 2

在当前数据模型中，您的查询应检查实际值（而不是节点的存在）。例如：

FirebaseDatabase.getInstance().getReference()
    .child("Trial").child("AvailableDisciplines")
    .orderByChild("Disciplines/EE/disciplineCode").equalTo("EE")
    ...

现在您有了一个实际的属性，可以在以下位置定义索引：

{
  "rules": {
    "Trial": {
      "AvailableDisciplines": {
        "$collegecode": {
          "Disciplines": {
            "$discipline": {
              ".indexOn": "disciplineCode"
            }
          }
        }
      }
    }
  }
}

Firebase数据库“ DeepQuery”，我的.indexOn规则是什么？

2 个答案: