I'm currently creating a dashboard application for my main application, this dashboard is able to display in charts the demography of the users that uses the app. I use Firebase Database as the backend. The JSON tree of my DB is as shown below. My question is, how do I get the amount of data with a specific value of a key? Example: the number of children with the value 'Pria' for the key 'jk' is 2.
My Backend JSON Tree:
So far, I'm able to get all of the data using:
DatabaseReference itemRef = FirebaseDatabase.instance.reference().child('data_pengguna');
And I've also tried the codes below, but it doesn't seem to work:
int jmlPria;
FirebaseDatabase.instance
.reference()
.child('data_pengguna')
.orderByChild('jk')
.equalTo('Pria')
.once()
.then((onValue) {
Map data = onValue.value;
jmlPria = data.length;
});
But I haven't successfully filtered the data and put it inside a variable, can anyone help me?
Many thanks in advance.
That last snippet looks correct, jmlPria should have the number of children.
But the value of jmlPria will only be set to the latest value inside the then() callback. Make sure that Text($jmlPria) is inside the then() callback. Outside of that, jmlPria will not have the correct value.
Also see Doug's great blog post on asynchronous programming.
Related
I will first say that I am a firmware developer trying to make a web interface for a personal project. My question might be basic as this is my first web interface with a database. I have searched quite a bit on how to achieve what I am trying to do without success, so I suspect I am not approaching this the right way, but here it is:
Basically I have a device pushing data to a firebase realtime database :
the push function generates an unique Id for me automatically which is nice...
Now In my flutter interface, I want to display the latest entry on a widget so I am using the onChildAdded functionnality of flutterfire:
ref.onChildAdded.listen((DatabaseEvent event) {
print(event.snapshot.key);
print(event.snapshot.value);
});
My first issue is that this function is triggered for all the child at first before waiting for new ones which is unnecessary and could be a problem when I begin to have a lot of data. Is there a way to simply get the latest sample and still get an event when one is added? (I still want to keep the old data to be able to make charts with them)
My second problem is the format of the received data:
{
-Mx2PCeptLf2REP1YFH0: {
"picture_url": "",
"time_stamp": "2022-02-28 21:56:58.502005",
"temperature": 27.71,
"relative_humidity": 42.77,
"eco2": 691,
"tvoc": 198,
"luminosity": 4193,
"vpd": 1.71
}
}
before using the put method, I didn't have the automatically generated ID so I was able to cast this as a Map<String, dynamic> and use the data like this in my widget:
Text(snapshot.data!["temperature"].toString())
but now the added nesting with the generated id is giving me a headache as I can't seem to figure out how to simply get the data.
So if anyone could help me to always get the single latest data when subscribing to a collection and how to access that data within my State of my StatefulWidget that would be much appreciated!
My first issue is that this function is triggered for all the child at first before waiting for new ones which is unnecessary and could be a problem when I begin to have a lot of data.
The Firebase Realtime Database synchronizes the state of the path/query that you listen to. So it doesn't just fire an event on onChildAdded for new data, but also for any existing data that you request. There is (intentionally) no way to change that behavior.
So your options here are limited:
You can remove the data that your application has processed, so that it doesn't get passed to the clients again. That means you essentially implement a message-passing mechanism on top of Firebase's data-synchronization semantics.
You can use a query to only request a certain subset of the child nodes at a path. For example, if you remember the latest key that you've received, you can get data from there on with ref.orderByKey().startAt("-Mx2LastKeyYouAlreadySaw").
Since this comes up regularly, I recommend also checking:
How can I setup Firebase to observe only new data?
How to get only updated data Firebase
How to fetch only latest specific data from Firebase?
and more from these search results
My second problem is the format of the received data:
The screenshot of your database shows two keys, each of which has a single string value. The contents of that value may be JSON, but the way they are stored is just a single string.
If you want to get a single property from the JSON, you either have to:
Decode the string back into JSON with jsonDecode.
Fix the problem at the source by storing the data as proper JSON, rather than as a string.
Firebase Realtime Database Overrides my Data at a location even when I use .push() method. The little-concrete knowledge I have about writing to Firebase Realtime database is that writing to Firebase real time database can be done in few several ways. Two of the most prominent are the
set() and 2. push() method.
The long story short, push() is used to create a new key for a data to be written and it adds data to the node.
So fine, firebase has being co-operating with me in my previous projects but in this, I have no idea what is going on. I have tried different blends of push and set to achieve my goal but no progress so far.
In the code below, what I want to achieve is 2 things, write to a location chatUID, message and time only once, but write severally '-MqBBXPzUup7czdG2xCI' all under the same node "firebaseGeneratedId1" ->
A better structure is below.
Help with code. Thanks.
UPDATE
Here is my code
The writers reference
_listeningMsgRef = _msgDatabase
.reference()
.child('users')
.child(userId)
.child('chats')
.child(chatUIDConcat);
When a user hits sendMessage, here is the function called
void sendMessage() {
_messageController.clear();
var timeSent = DateTime.now().toString();
//Send
Map msgMap = {
'message': msg,
'sender': userId,
'time': timeSent,
'chatUID': chatUIDConcat
};
//String _key = _listeningMsgRef.push().key;
_listeningMsgRef.child(chatUIDConcat).set().whenComplete(() {
SnackBar snackBar = const SnackBar(content: Text('Message sent'));
ScaffoldMessenger.of(context).showSnackBar(snackBar);
DatabaseReference push = _listeningMsgRef.child(chatUIDConcat).push().set(msgMap);
});
}
The idea about the sendMessage function, is to write
chatUID:"L8pacdUOOohuTlifrNYC3JALQgh2+q5D38xPXVBTwmwb5Hq..."
message: "I'm coming"
newMessage: "true"
sender: "L8pacdUOOohuTlifrNYC3JALQgh2"
When it is complete, then push new nodes under the user nodes.
EDIT:
I later figured out the issue. I wasn't able to achieve my goal because I was a bit tensed while doing that project. The issue was I was wanted to write new data into the '-MqBBXPzUup7czdG2xCI' node without overwriting the old data in it.
The solution is straight forward. I just needed to ensure I wrote data in that node as new nodes under it. Nothing much, thanks
Frank van Puffelen for your assistance.
Paths in Firebase Realtime Database are automatically created when you write any data under then, and deleted when you remove the last data under them.
So you don't need to first create the node for the chat room. Instead, it gets auto-created when you write the first message into it with _listeningMsgRef.child(chatUIDConcat).push().set(msgMap)
I have been trying to get arrays working in Firebase, and I am aware that there are a lot of references and discussions about this online, and I have read through all of these and none of it works.
First off, the Firebase side. The structure containing the array and two example strings inside it:
Firebase Structure
collection -> document -> fields
userData profileImages URLs (array)
: https://firebasestorage.googleapis.com/v0/b/app-138804.appspot.com/o/jRwscYWLs1DySLMz7jn5Yo2%2Fprofile%2Fimage_picker4459623138678.jpg?alt=media&token=ec1043b-0120-be3c-8e142417
: https://firebasestorage.googleapis.com/v0/b/app-138804.appspot.com/o/jRwscYWLs3872yhdjn5Yo2%2Fprofile%2Fimage_picker445929873mfd38678.jpg?alt=media&token=ec3213b-0120-be9c-8e112632
The first issue I am facing is writing to this array in the database:
Firestore.instance.collection('userData').document('profileImages').updateData({
'URLs': _uploadedFileURL,
});
Whenever I add data to this array, it just overwrites the existing data. I need to be able to keep all the existing data intact and simply add the current new line to the array.
Once this is working, I then need to be able to return all of the strings in this array without needing to know how many of them there will be.
For this part, I basically have nothing at this point. I could show some of the things I have tried based on suggestions from other articles on this, but none of it is even close to working correctly.
im assuming that _uploadedFileURL is a String, and you are updating the property URLs, that's why your data gets overwritten, because you are changing the URLs value to a single string which is _uploadedFileURL. to solve this issue, simply get the current data inside profileImages before commiting the update. like so
final DocumentSnapshot currentData = await Firestore.instance.collection('userData').document('profileImages').get();
Firestore.instance.collection('userData').document('profileImages').updateData({
'URLs': [
...currentData.data['URLs'],
_uploadedFileURL
],
});
and for the second part of your question, all you need is to query for the profileImages
Future<List<String>> _getProfileImages() {
final document = Firestore.instance.collection('userData').document('profileImages').get();
return document.data['profileImages]
}
the result of the get method will be a DocumentSnapshot, and inside the data property will access the profileImages which is a List<String>.
Ok guys and girls I have worked this out. Part 1: appending data to an array in Firebase.
Firestore.instance.collection('userData').document('profileImages').updateDataupdateData({
'URLs':FieldValue.arrayUnion([_uploadedFileURL]),
});
Where _uploadedFileURL is basically a string, for these purposes. Now I have read that arrayUnion, which is super groovy, is only available in Cloud Firestore, and not the Realtime Database. I use Cloud Firestore so it works for me but if you are having issues this might be why.
Now what is extra groovy about Cloud Firestore is that you can similarly remove an element from the array using:
Firestore.instance.collection('userData').document('profileImages').updateDataupdateData({
'URLs':FieldValue.arrayRemove([_uploadedFileURL]),
});
So how to get this data back out again. A simple way I have found to get that data and chuck it into a local array is like so:
List imageURLlist = [];
DocumentReference document = Firestore.instance.collection('userData').document('profileImages');
DocumentSnapshot snapshot = await document.get();
setState(() {
imageURLlist = snapshot.data['URLs'];
});
From here at least you have the data, can add to it, can remove from it and this can be a platform for you to figure out what you want to do with it.
I'm using Firebase's Firestore to store and publish new events.
In the code below, I'm subscribing to a collection and want to be notified when a new items is added (this code is executing on a browser).
When I first connect, I would like to receive a true snapshot. However, once I'm connected to Firestore and have received an initial snapshot, with each new item, I only want to get the udpates, not the whole collection over and over again!
function queryExercise(exercise){
db.collection("exercises").where("exercise","==",exercise).onSnapshot(function(querySnapshot){
querySnapshot.forEach(function(doc){
var d_ = doc.data()
console.log(d_);
...do somethign with d_...
})
})
}
When I publish a new item to the collection, my console is full of all events received earlier...in other words, it is sending me the full snapshot, instead of just the deltas.
Am I doing something wrong or does the API really not support delta updates?
Looks like I needed to read on docChanges:
function queryExercise(exercise){
db.collection("exercises").where("exercise","==",exercise).onSnapshot(function(querySnapshot){
// \/-----this thing
querySnapshot.docChanges().forEach(function(change){
var d_ = change.doc.data()
console.log("Change type:", change.type, d_);
...
});
})
}
From https://firebase.google.com/docs/firestore/query-data/listen
That's the way Firestore queries work. If you don't provide a filter for which documents you want in a collection, you will get all the documents in that collection. The only way to change this behavior is to provide a filter in your query using a where clause.
It sounds like you have a thought in mind about what makes for a "new" document in your collection. You will need to represent that using some field in the documents in your collection. Usually this will be a timestamp type field that's added or modified whenever a document is created or changed. This will be part of your where clause that determines what's "new". Use this field as a filter to find out what's new.
I'm having a really hard time understanding how Nosql works so I hope someone can help me understand it a bit better.
I'm trying to make a simple chat application (One to one chat support and chat groups) and want to dislay a list of all the conversations that the current user is in. This is my table for it.
I tried getting the data in several ways. But what I currently have is this (Which should work according to the internet, but doesn't).
_membersRef.equalTo(1508, key: '1508').once().then((DataSnapshot snap) {
print(snap.value);
});
I also tried
_membersRef.startAt(1508).endAt(1508).once().then((DataSnapshot snap) {
print(snap.value);
});
What I want my code to do is return all records that have my account_id in them (1508 in this case). So it should return the record "one".
So if I change the uid in the code to 1509 it should return "One" and "two". How can I make this happen?
To get the key one try this:
_membersRef.orderByChild('1508').equalTo(true).once().then((DataSnapshot snap) {
print(snap.value);
});
the snapshot is at child members then you order it according to child 1508 which is equalTo(true).