How to add if else condition to data in Realtime Database in Flutter? - flutter

Question

Currently, I am working on a Flutter project, which is a tricycle booking system. Right now, I want to implement the functionality of having life points for every account. I have thought of this for some time and I have decided to store a value in the real-time database in firebase, it is where I will be decrementing the life points every time a user cancels the booking. What I want to do right now, is to check if the value stored in lifePoints is equal to a certain value, if yes, then I will be placing some functions and restrictions in there. So, how do i get the data from realtime database using flutter and add conditions to it?
Any help will be much appreciated. Thank you!

Answer 1

If you want to read data from Firebase, the documentation on reading data is a great starting point.
From there comes this great example of reading data once:
final ref = FirebaseDatabase.instance.ref();
final snapshot = await ref.child('users/$userId').get();
if (snapshot.exists) {
print(snapshot.value);
} else {
print('No data available.');
}
And this example for listening for data, which provides both the current value right away, and then continues to listen for updates:
DatabaseReference starCountRef =
FirebaseDatabase.instance.ref('posts/$postId/starCount');
starCountRef.onValue.listen((DatabaseEvent event) {
final data = event.snapshot.value;
updateStarCount(data);
});
If you want to increment/decrement a value in the database, have a look at this example from the documentation on atomic increments/decrements:
void addStar(uid, key) async {
Map<String, Object?> updates = {};
updates["posts/$key/stars/$uid"] = true;
updates["posts/$key/starCount"] = ServerValue.increment(1);
updates["user-posts/$key/stars/$uid"] = true;
updates["user-posts/$key/starCount"] = ServerValue.increment(1);
return FirebaseDatabase.instance.ref().update(updates);
}
Or if you want to perform a more complex update of a value based on its current value, you'll want to use a transaction:
DatabaseReference postRef =
FirebaseDatabase.instance.ref("posts/foo-bar-123");
TransactionResult result = await postRef.runTransaction((Object? post) {
// Ensure a post at the ref exists.
if (post == null) {
return Transaction.abort();
}
Map<String, dynamic> _post = Map<String, dynamic>.from(post as Map);
if (_post["stars"] is Map && _post["stars"][uid] != null) {
_post["starCount"] = (_post["starCount"] ?? 1) - 1;
_post["stars"][uid] = null;
} else {
_post["starCount"] = (_post["starCount"] ?? 0) + 1;
if (!_post.containsKey("stars")) {
_post["stars"] = {};
}
_post["stars"][uid] = true;
}
// Return the new data.
return Transaction.success(_post);
});
As you might notice these are all code snippets from the documentation, all from the same page even. I recommend spending some time studying that documentation, and then trying to apply these to your own use-case. If you then run into problems while implementing the use-case, post a question with the minimal code that reproduces where you got stuck and we can probably help further.