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A month of Flutter: WIP save users to Firestore

Abraham Williams
Developer Advocate at Google | He/him
Originally published at ・3 min read

Originally published on

Today was supposed to be simple. Take form values, save them in Firestore. It works but the current implementation is messy so I'm going to walk through the work in progress (WIP) code and refactor it tomorrow.

The larger architectural change was creating a UserService to handle getting and creating users. This approach works but creates a complex dependency injection pattern that requires a lot of duplicate code and mocking in test. These are some of the current changes and what I don't like about the implementation:

RegisterPage now takes a UserService which in turn takes FirebaseAuth and Firestore instances. Doing this once wouldn't be so bad but I've had to instantiate UserService in several places. I'd like to find a better approach than UserService.

  userService: UserService(
    firebaseAuth: FirebaseAuth.instance,
    firestore: Firestore.instance,
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RegisterForm was updated to call on submit if the form is valid. _submit will also grab photoUrl and set it directly on _formData.

Future<void> _submit() async {
  if (_formKey.currentState.validate()) {;
    _formData['photoUrl'] = widget.firebaseUser.photoUrl;

    final bool result =
        await widget.userService.addUser(widget.firebaseUser.uid, _formData);
    if (result) {
      _showSnackBar(context, 'Welcome ${_formData['fullName']}');
      Navigator.pushNamed(context, HomePage.routeName);
    } else {
      _showSnackBar(context, 'Error submitting form');
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_formData['key'] is clumsy so I'd like to refactor it to use _formData.key instead. The onSaved callback on TextFormField takes the input value and sets it on _formData.

  initialValue: widget.firebaseUser.displayName,
  decoration: const InputDecoration(
    labelText: 'Full name',
    validator: (String value) {
      if (value.trim().isEmpty) {
      return 'Full name is required';
  onSaved: (String value) => _formData['fullName'] = value,
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RegisterForm now takes a FirebaseUser and a UserService. You might notice the repetitiveness repetitiveness of UserService. The FirebaseUser is used to pre-fill the form name fields so users can just submit the form if they want to use their Google registered names.

Here is how RegisterForm is called in RegisterPage:

Widget _formWhenReady() {
  return _firebaseUser == null
      ? const CircularProgressIndicator()
      : RegisterForm(
          firebaseUser: _firebaseUser,
          userService: UserService(
            firestore: Firestore.instance,
            firebaseAuth: FirebaseAuth.instance,
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RegisterPage has a new _getCurrentUser method that will set the _firebaseUser state. Until _firebaseUser is set, CircularProgressIndicator is displayed. Checking if there is a current user is going to happen a lot in the application so this needs to be much simpler to do.

Future<void> _getCurrentUser() async {
  final FirebaseUser user = await widget.userService.currentUser();
  setState(() {
    _firebaseUser = user;
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UserService itself is fairly simple.

class UserService {
    @required this.firestore,
    @required this.firebaseAuth,

  final Firestore firestore;
  final FirebaseAuth firebaseAuth;

  Future<FirebaseUser> currentUser() {
    return firebaseAuth.currentUser();

  Future<bool> addUser(String uid, Map<String, String> formData) async {
    try {
      await firestore
      return true;
    } catch (e) {
      return false;

  Map<String, dynamic> _newUserData(Map<String, String> formData) {
    return <String, dynamic>{}
      ..addAll(<String, dynamic>{
        'agreedToTermsAt': FieldValue.serverTimestamp(),
        'createdAt': FieldValue.serverTimestamp(),
        'updatedAt': FieldValue.serverTimestamp(),
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It takes Firestore and FirebaseAuth instances so that it can get the currentUser or create a new document with setData. I don't like having to inject UserService in multiple places and I would like to cleanup the formData type.

FieldValue.serverTimestamp() is a special Firestore value that will use the server timestamp when the document gets saved.

In the tests I'm now having to mock a lot more stuff. This is making the tests more verbose and harder to read and change. Come back tomorrow to see the exciting conclusion of the refactor.

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