Firebase android : make username unique -

parse shut down @ end of year, decided start using firebase. need implement register process 3 fields : email, username, password (email & username must unique app).

since, firebase not providing easy way manage username parse, decided use email/password registration , save additional data username. here users data structure :

app : {     users: {        "some-user-uid": {             email: "test@test.com"             username: "myname"        }     } } 

but, want make username unique , check before creating account. these rules :

{     "rules": {         ".read": true,         ".write": true,         "users": {             "$uid": {                 ".write": "auth !== null && auth.uid === $uid",                 ".read": "auth !== null && auth.provider === 'password'",                 "username": {".validate": "!root.child('users').child(newdata.child('username').val()).exists()"}             }         }    } } 

thank help

part of answer store index of usernames, check against in security rules:

app : {     users: {        "some-user-uid": {             email: "test@test.com"             username: "myname"        }     },     usernames: {         "myname": "some-user-uid"     } } 

so usernames node maps username uid. reads "username 'myname' owned 'some-user-uid'".

with data structure, security rules can check if there entry given username:

"users": {   "$uid": {     ".write": "auth !== null && auth.uid === $uid",     ".read": "auth !== null && auth.provider === 'password'",     "username": {       ".validate": "         !root.child('usernames').child(newdata.val()).exists() ||         root.child('usernames').child(newdata.val()).val() == $uid"     }   } } 

this validates username isn't claimed yet or claimed current user.