firebase web - update database where a certain value is found - firebase

Question

My database looks as below :
I need to update the division_name where the index_num is 3.
I tried the following code but it did not work -
var division_index_found="3";
var division_name_given="new div";
var query_update=firebase.database().ref("/divisions")
.orderByChild('index_num').equalTo(division_index_found);
query_update.once("child_added", function(snapshot) {
snapshot.ref.update({ division_name: division_name_given });
});
What approach to adopt here ?
EDIT1:
I get warning in chrome console :
FIREBASE WARNING: Using an unspecified index. Consider adding ".indexOn": "index_num" at /divisions to your security rules for better performance
EDIT2:
From the firebase database the districts node (?) looks like :
"districts" : {
"-KbVYCSO8wrMoXD3vL81" : {
"district_name" : "Rangpur",
"division_index" : "3",
"index_num" : 2
},
"-KbVYHgbWMDMtGsnmvei" : {
"district_name" : "jessore",
"division_index" : "3",
"index_num" : 3
},
"-KbVYKtSnPMFDkx9z0cU" : {
"district_name" : "district 1",
"division_index" : "3",
"index_num" : 4
}
}
Now I want to update district_name for a certain index_num and division_index. I use the following code :
var district_index="3";
var division_index="3"
var district_index_parsed = parseInt(district_index);
var query_update=firebase.database().ref("/districts")
.orderByChild('index_num').equalTo(district_index_parsed);
query_update.once("child_added", function(snapshot) {
snapshot.forEach(function(snapshot_indiv){
if(parseInt(snapshot_indiv.division_index)==parseInt(division_index)){
var district_name_again="new district name";
snapshot_indiv.ref.update({ district_name: district_name_again },function(error){
});
}// end of if division_index compare
});// end of forEach
});// end of query_update once
But the console shows :
Uncaught Error: No index defined for index_num
at je.get (firebase-database.js:94)
...
...
at edit_districts.php:359
...
which ultimately hints at the following line of code in my edit_districts.php file:
snapshot.forEach(function(snapshot_indiv){
inside the query_update.once part.The forEach method seems to make the problem.
And the security rules are defined as
{
"rules": {
".read": "auth != null",
".write": "auth != null",
"divisions": {
".indexOn": "index_num"
},
"districts": {
".indexOn": "index_num"
},
}
}
How to get rid of the error to update the database ?

Answer 1

You'll need to add an index to your Firebase Database security rules. I recommend reading the Firebase documentation on security rules, specifically the section on indexes.
From the documentation comes this first sample:
{
"rules": {
"dinosaurs": {
".indexOn": ["height", "length"]
}
}
}
Modified to your data structure, it'll look something like this:
{
"rules": {
"divisions": {
".indexOn": "index_num"
}
}
}