Why document doesn't exist. But all time !snapshot.hasData is false

Question

I make sign up system and managing user information.

When sign-up, users are required to write user name, and it's stored in firestore.

User data are stored like this;

And trying to get userName with the code;

CollectionReference users = FirebaseFirestore.instance.collection('users');

return FutureBuilder<DocumentSnapshot>(
  future: users.doc(FirebaseAuth.instance.currentUser!.uid).get(),
  builder:
      (BuildContext context, AsyncSnapshot<DocumentSnapshot> snapshot) {
    if (snapshot.hasError) {
      return Text("Something went wrong");
    }

    print("${!snapshot.hasData} ${!snapshot.data!.exists}"); // always "false true"
    if (!snapshot.hasData && !snapshot.data!.exists) {
      return Text("Document does not exist");
    }

    if (snapshot.connectionState == ConnectionState.done) {
      Map<String, dynamic> data =
          snapshot.data!.data() as Map<String, dynamic>;
      return Text("User Name: ${data['userName']}");
    }

    return const CircularProgressIndicator();
  },
);

However always return Text("Document does not exist"); is called, and userName is not displayed.

Why doesn't userName returned? I searched for a misspelling but couldn't find it. This issue has taken a lot of time today. Thank you.

Frank van Puffelen · Accepted Answer · 2021-09-23T14:19:21.383

The snapshot.data that you are referring to is the AsyncSnapshot that is used to monitor the status of the asynchronous operation. Its hasData becomes true when the asynchronous operation has completed: so when it is done reading the DocumentSnapshot from the database.

To detect whether the DocumentSnapshot actually exists, you need to check its exists property.

A quick summary of common statuses:

Object.property	Value	Explanation
`AsyncSnapshot.hasData`	`false`	the asynchronous operation has either not yet completed, or did not result in a `DocumentSnapshot` (for example: if there was a network error). Calling `snapshot.data` will result in an error message.
`AsyncSnapshot.hasData`	`true`	the asynchronous operation has completed and you can safely call `snapshot.data` on it to get the `DocumentSnapshot`.
`DocumentSnapshot.exists`	`false`	the document you requested does not exist, and calling `document.data` on the snapshot will result in an error.
`DocumentSnapshot.exists`	`true`	the document you requested exists, and you can access its data.

So your !snapshot.hasData will be false once the AsyncSnapshot is done loading the DocumentSnapshot. To determine whether the document actually exists, use snapshot.hasData && snapshot.data!.exists.

I also recommend checking out my explanation here of the various types of snapshots in Flutter code: What is the difference between existing types of snapshots in Firebase?

Thank you very much. But I can't still understand why `DocumentSnapshot.exists` always `false`. I checked misspelling again and again, and It's exist in firestore fields. — Beginner_, Sep 24 '21 at 03:36

score 1 · Answer 2 · answered Sep 23 '21 at 13:04

1

Miss to use ! before snapshot.hasData

if (!snapshot.hasData && !snapshot.data!.exists) {
      return Text("Document does not exist");
    }

answered Sep 23 '21 at 13:04

Jahidul Islam

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Thank you. I tried it, this `if` statement ignored but snapshot was really empty. `print("${!snapshot.hasData} ${!snapshot.data!.exists}");` result is `false true`. Why I can't get data? – Beginner_ Sep 23 '21 at 13:14
what about your document id? – Jahidul Islam Sep 23 '21 at 13:30
It's user uid. doc() is equal to doc(FirebaseAuth.instance.currentUser!.uid) so I wrote so. – Beginner_ Sep 23 '21 at 13:33

Why document doesn't exist. But all time !snapshot.hasData is false

2 Answers2