Retrieving child record when parent key is unknown in Firebase

Question

I have a data like this:

"customers": {
    "aHh4OTQ2NTlAa2xvYXAuY29t": {
        "customerId": "xxx",
        "name": "yyy",
        "subscription": "zzz"
    }
}

I need to retrive a customer by customerId. The parent key is just B64 encoded mail address due to path limitations. Usually I am querying data by this email address, but for a few occasions I know only customerId. I've tried this:

getCustomersRef()
   .orderByChild('customerId')
   .equalTo(customerId)
   .limitToFirst(1)
   .once('child_added', cb);

This works nicely in case the customer really exists. In opposite case the callback is never called.

I tried value event which works, but that gives me whole tree starting with encoded email address so I cannot reach the actual data inside. Or can I?

I have found this answer Test if a data exist in Firebase, but that again assumes that you I know all path elements.

getCustomersRef().once('value', (snapshot) => {
    snapshot.hasChild(`customerId/${customerId}`);
});

What else I can do here ?

Update

I think I found solution, but it doesn't feel right.

let found = null;
snapshot.forEach((childSnapshot) => {
    found = childSnapshot.val();
});
return found;

Answer 1

old; misunderstood the question :

If you know the "endcodedB64Email", this is the way.:

var endcodedB64Email = B64_encoded_mail_address;

firebase.database().ref(`customers/${endcodedB64Email}`).once("value").then(snapshot => {
       // this is getting your customerId/uid. Remember to set your rules up for your database for security! Check out tutorials on YouTube/Firebase's channel.
       var uid = snapshot.val().customerId;
       console.log(uid) // would return 'xxx' from looking at your database

// you want to check with '.hasChild()'? If you type in e.g. 'snapshot.hasChild(`customerId`)' then this would return true, because 'customerId' exists in your database if I am not wrong ...
});

UPDATE (correction) :

We have to know at least one key. So if you under some circumstances only know the customer-uid-key, then I would do it like this.:

// this is the customer-uid-key that is know. 
var uid = firebase.auth().currentUser.uid; // this fetches the user-id, referring to the current user logged in with the firebase-login-function
// this is the "B64EmailKey" that we will find if there is a match in the firebase-database
var B64EmailUserKey = undefined;

// "take a picture" of alle the values under the key "customers" in the Firebase database-JSON-object
firebase.database().ref("customers").once("value").then(snapshot => {
     // this counter-variable is used to know when the last key in the "customers"-object is passed
     var i = 0;
     // run a loop on all values under "customers". "B64EmailKey" is a parameter. This parameter stores data; in this case the value for the current "snapshot"-value getting caught
     snapshot.forEach(B64EmailKey => {
          // increase the counter by 1 every time a new key is run
          i++;
          // this variable defines the value (an object in this case)
          var B64EmailKey_value = B64EmailKey.val();
          // if there is a match for "customerId" under any of the "B64EmailKey"-keys, then we have found the corresponding correct email linked to that uid
          if (B64EmailKey_value.customerId === uid) {
               // save the "B64EmailKey"-value/key and quit the function
               B64EmailUserKey = B64EmailKey_value.customerId;

               return B64UserKeyAction(B64EmailUserKey)
          }

          // if no linked "B64EmailUserKey" was found to the "uid"
          if (i === Object.keys(snapshot).length) {
               // the last key (B64EmailKey) under "customers" was returned. e.g. no "B64EmailUserKey" linkage to the "uid" was found
               return console.log("Could not find an email linked to your account.")
          }
     });
});

 // run your corresponding actions here
 function B64UserKeyAction (emailEncrypted) {
      return console.log(`The email-key for user: ${auth.currentUser.uid} is ${emailEncrypted}`)
 }

I recommend putting this in a function or class, so you can easily call it up and reuse the code in an organized way.

I also want to add that the rules for your firebase must be defined to make everything secure. And if sensitive data must be calculated (e.g. price), then do this on server-side of Firebase! Use Cloud Functions. This is new for Firebase 2017.