How do i create a timeline feed using firebase in flutter? - firebase

Question

- posts
- userID
- userID
- randomID
- randomID
- followers
- personB userid
- personA userid
- following
- personA userid
- personB userid
This is how my firebase collection is organized.
how do i get create a timeline feed for current logged-in user where the timline posts should be of only from the logged-in user's following list?
Note:I dont want to use firebase functions.Is it possible with CRUD?
What ive tried so far.
getFollowing() async {
QuerySnapshot snapshot = await followersRef
.document(currentUser.id)
.collection('userFollowing')
.getDocuments();
setState(() {
followingList = snapshot.documents.map((doc) => doc.documentID).toList();
print(followingList);
});
}
getTimeline()async{
QuerySnapshot snapshot = await postsRef
.document(followingList)//getting an error here saying list<string> csn't be assigned to string.
.collection('userPosts')
.orderBy('timestamp', descending: true)
.getDocuments();
List<Post> posts =
snapshot.documents.map((doc) => Post.fromDocument(doc)).toList();
setState(() {
this.posts = posts;
});
}

Answer 1

The approach which I think is efficient is using A collection 'Posts' and document for each post, with an array inside the post document as a field.
This means when a user adds post you have to include the user's followers as a field(List<dynamic) inside the post.
- posts(Collection)
- post(Document)
- followers(List<dynamic>)
you can query post for users like
Firestore.instance.collection('posts').where('followers', arrayContains: currentUserId).snapshots();
//this brings all queries with the tagged users as followers aka the users that follow the poster will be able to query this post.
if you want to update the array you can use
FieldValue.arrayRemove or FieldValue.arrayUnion,
Edit: As a final warning I must mention that there is a limit to how much data there could be for one document, based on the scale of your app you have to decide whether to put a growing list (such as followers) inside one document or to create another collection for the growing list and give one document for each element since documents can't be limited (this approach could cost more).

Answer 2

List timelinePosts =[];
getFollowing() async {
QuerySnapshot snapshot = await followersRef
.document(currentUser.id)
.collection('userFollowing')
.getDocuments();
setState(() {
followingList = snapshot.documents.map((doc) => doc.documentID).toList();
print(followingList);
});
}
getTimeline()async{
List posts = [];
for( int i=0; i< followingList.length; i++)
{
QuerySnapshot snapshot = await postsRef
.collections('posts/${followingList[i]}/userPosts')
.orderBy('timestamp', descending: true)
.getDocuments();
posts+= snapshot.data.documents.map((doc) => {'id':doc.documentID,...doc.data}).toList();
}
setState(() {
timelinePosts = timeLinePosts + posts;
});
}
then u can use Listview.builder() on timelinePosts,
However this is not the most efficient method, since you are fetching all the posts at once. You can also implement fetch post as you scroll through the list, using Listview controller attribute