如何在我的 flutter firebase 应用程序中检查用户名可用性

Question

I am trying to check if a username is already taken in my flutter and firebase app, but I am facing some problems. I am able to query the user's collection and compare a name string saved in the input of the text form with names already in the database, which works perfectly well. But my problem is when a user takes a name and that same user tries to save his profile without changing his name, he gets the message username is already taken, meaning he can't save his profile cause he has already taken his own name. I want a solution where a user can save his profile if he or she hasn't modified his or her username without going through the username is already taken process. I don't know if it's possible to add an if statement to check if the current user name is equal to the username in the text field? or help with any solution that works. please these are my codes below

//checks fields of user collection and compares the 
 //string _username with the userName of each user.
 final QuerySnapshot result = await Firestore.instance
      .collection('users')
      .where('userName', isEqualTo: _userName)
      .getDocuments();

    //converts results to a list of documents
  final List<DocumentSnapshot> documents = 
 result.documents;

  //checks the length of the document to see if its 
   //greater than 0 which means the username has already been taken 
   the name
if (documents.length > 0) {
    print(_userName + ' is already taken choose 
    another name');
 }else{
   print(_userName + ' are you sure you want to use 
    this name');
  }

Answer 1

I think a solution would to only check to see if this username is taken if the user changes his username. Therefore you would not have to worry if the user with the taken username is just saving his profile without changing his username.

Answer 2

yes if you are in firestore as backend...you can not show query stream in registration page for username suggestions for availability bcoz u hav to set firestore rules insecure and allow unauthorised users to read write your database...so better to push a new page after that registration page where you can place field for username in this case you are already registered and logged in so firestore security rule will not invade.... Happy coding:)