Do cloud firestore snapshot reads all the documents in the collection? - firebase

Question

I'm creating a chat screen. What I'm currently doing is that I'm using a Streambuilder to listen to the 'messages' collection and display the messages using ListView.builder().
Below is the code i'm using.
StreamBuilder<QuerySnapshot>(
stream: _fireStoreInstance
.collection('$collectionName/$docID/messages')
.orderBy('sentAt', descending: true)
.snapshots(),
builder: (context, snapshot) {
if (snapshot.connectionState == ConnectionState.waiting)
return Center(
child: CircularProgressIndicator(),
);
List<Map> documents = snapshot.data.docs
.map((doc) => {'documentId': doc.id, ...doc.data()})
.toList();
return ListView.builder(
cacheExtent: MediaQuery.of(context).size.height,
reverse: true,
itemCount: documents.length,
padding:
const EdgeInsets.only(left: 15.0, right: 15.0, bottom: 5.0),
itemBuilder: (context, index) {
return MessageBubble(
...
);
},
);
},
),
My concern is, will the query fetch all the documents in the collection all at once? If yes then it will be a lot of reads each time the query is executed
_fireStoreInstance
.collection('$collectionName/$docID/messages')
.orderBy('sentAt', descending: true)
.snapshots();
Do I need to paginate by using limit ? If I paginate how do I listen to new messages ? Thank you for your help.

Answer 1

Yes, .snapshots() will read and keep listening to all documents that fit the query, if you want a subset of that you will have to paginate it using .limit().
I have found this article, with a video step by step on How to perform real-time pagination with Firestore with the use of an infinite scroll. I think this is exactly what you looking for, so I won't post any code since you can follow that example.