I want to use the following code to get data from firestore that is sorted according to the date the document was updated on:
fun getQuery(groupID: String): Query {
val path = FirestorePath()
return path.getTaskCollectionRef()
.orderBy(ActionTask.FieldNames.taskUpdatedOn.name, Query.Direction.DESCENDING)
.whereEqualTo(ActionTask.FieldNames.taskGroupID.name, groupID)
.whereEqualTo(ActionTask.FieldNames.taskOpen.name, true)
}
The problem is that the .orderBy() causes my app to display data from documents that are deleted (existed previously, now deleted).
When I remove the .orderBy(), I see the correct data in my app.
This is due to the offline mode of Firestore being active by default in your code. You should turn if off in order to avoid getting responses from the cache instead of your database.
You can find more information about the offline mode and how to disable it for Android over at this document
Hope you find this useful!
Let say I have 100 items (actually it's much more than 100 in reality) stored in Firebase Realtime Database. So I decided to use pagination, I use the Query#addValueEventListener() function for query and only load 20 items each request, the last queried item's key passed to the Query#startAt() to get the next 20 items. It worked well so far
But the problem is after I reach the last item (the 100th item) in Firebase Database, it will give me back all items (100 items) hold in Database for the next request.
Currently, I have to check the key id passed to Query#startAt() and the last queried item's key id are equal or not, if true then I was reach the end. Honestly I think this is not a nicely solution
So anyone here has better solutions for this case, please help me.
thanks in advance!
the code here
private var lastKey: String? = null
fun requestItems(startAtId: String?){
val query = dbRef.orderByKey()
if(!startAtId.isNullOrBlank()){*the problem here*
query.startAt(startAtId)
}
query.limitToFirst(10)
query.addValueEventListener(object : ValueEventListener{
override fun onDataChange(dataSnapshot: DataSnapshot) {
val lastKey = it.children.last().key
if (lastKey.equals(startAtId)){
//has reached the last item
//ignore the result
}else{
//do something with the result
lastKey = latestKey
}
}
override fun onCancelled(dataSnapshot: DatabaseError) {
}
})
}
update
I just realized the problem I was faced is at initializing the Query object (1st line to 5th line) in the requestItems() function. It always returns whole items from db. I changed that initializing block to the bellow block. I don't know any different from them but it worked as pagination.
val query = if(startAtId.isNullOrBlank()){
dbRef.orderByKey()
}else{
dbRef.orderByKey()
.startAt(startAtId)
}.limitToFirst(10)
But there is still no sign to point out that it reach the last item in db. after reaching the end Firebase always returns the last item, I think that happened because of startAt(startAtId) function and there is no such a function like startAtAfter(startAtId)
I attach the json file here that is not real data in db, but they has same structure.
The Firebase Query object is immutable. Whenever you call one of the orderBy, startAt and other methods, it returns a new Query object. So you will need to capture that object in a variable:
val query = dbRef.orderByKey()
if(!startAtId.isNullOrBlank()){
query = query.startAt(startAtId)
}
query = query.limitToFirst(10)
...
That's also why your updated construct works: you've put all query-building into a single chain and capture the results. But while it works, I personally find the result less readable than the one above.
I need to have one problem sorted out. I want a cloud function, where I need to loop through every Posts that has uniqueID and I want to sort those uniqueID's according to the value of TotalReactions. To me more vivid, suppose, the first post has totalReactions = 5, and second one has totalReactions = 6, then I need to have another RealTimeDatabase "PostArranged" which sorts them in descending order, so second post which has Total Reaction would be in first and then follows the one which has lesser TotalReaction...
Here is how my firebase realtime database looks like:
Posts
-L29TD-nsUYRu3wYcCQl
Caption: "First Screenshot"
CurrentUserReaction: "notreacted"
Image: "https://firebasestorage.googleapis.com/v0/b/nep..."
ReactingUser
<user-id>:"1"
<user-id>:"2"
Time: "13:40:54"
TotalReactions: "2"
Unique: "-L29TD-nsUYRu3wYcCQl"
UserPhoto: "https://firebasestorage.googleapis.com/v0/b/nep..."
Username: "Me"
Any help would be appreciated ..
This is not a good way to do what you want to do. In this method the database has to be sorted to another "ArrangedDatabase" every time a reaction is added which will happen in a high frequency. So it will be very expensive to do this with Cloud Functions.
Instead use orderByChild(), orderByKey(), orderByValue() to sort data when you're querying data.
Sorting data - Firebase documentation this show it quite well.
For anyone who want to do this in your RecyclerViewAdapter provided by Firebase, it is easily done... When you pass in those 4 parameters. Do not pass the database Reference, instead, make a new query, and make sure to sort that thing either by OrderByChild(), OrderByValue() or anything you want to order by... i.e.
In my case, I will do something like this:
q = mDatabaseReference.orderByChild("TotalReactions");
and pass q as parameter inside FirebaseAdapter, like this:
FirebaseRecyclerAdapter<Posts,PostViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Posts, PostViewHolder>(
Posts.class, R.layout.each_post_layout , PostViewHolder.class, q
) {
.
}
I'm trying to test out Firebase to allow users to post comments using push. I want to display the data I retrieve with the following;
fbl.child('sell').limit(20).on("value", function(fbdata) {
// handle data display here
}
The problem is the data is returned in order of oldest to newest - I want it in reversed order. Can Firebase do this?
Since this answer was written, Firebase has added a feature that allows ordering by any child or by value. So there are now four ways to order data: by key, by value, by priority, or by the value of any named child. See this blog post that introduces the new ordering capabilities.
The basic approaches remain the same though:
1. Add a child property with the inverted timestamp and then order on that.
2. Read the children in ascending order and then invert them on the client.
Firebase supports retrieving child nodes of a collection in two ways:
by name
by priority
What you're getting now is by name, which happens to be chronological. That's no coincidence btw: when you push an item into a collection, the name is generated to ensure the children are ordered in this way. To quote the Firebase documentation for push:
The unique name generated by push() is prefixed with a client-generated timestamp so that the resulting list will be chronologically-sorted.
The Firebase guide on ordered data has this to say on the topic:
How Data is Ordered
By default, children at a Firebase node are sorted lexicographically by name. Using push() can generate child names that naturally sort chronologically, but many applications require their data to be sorted in other ways. Firebase lets developers specify the ordering of items in a list by specifying a custom priority for each item.
The simplest way to get the behavior you want is to also specify an always-decreasing priority when you add the item:
var ref = new Firebase('https://your.firebaseio.com/sell');
var item = ref.push();
item.setWithPriority(yourObject, 0 - Date.now());
Update
You'll also have to retrieve the children differently:
fbl.child('sell').startAt().limitToLast(20).on('child_added', function(fbdata) {
console.log(fbdata.exportVal());
})
In my test using on('child_added' ensures that the last few children added are returned in reverse chronological order. Using on('value' on the other hand, returns them in the order of their name.
Be sure to read the section "Reading ordered data", which explains the usage of the child_* events to retrieve (ordered) children.
A bin to demonstrate this: http://jsbin.com/nonawe/3/watch?js,console
Since firebase 2.0.x you can use limitLast() to achieve that:
fbl.child('sell').orderByValue().limitLast(20).on("value", function(fbdataSnapshot) {
// fbdataSnapshot is returned in the ascending order
// you will still need to order these 20 items in
// in a descending order
}
Here's a link to the announcement: More querying capabilities in Firebase
To augment Frank's answer, it's also possible to grab the most recent records--even if you haven't bothered to order them using priorities--by simply using endAt().limit(x) like this demo:
var fb = new Firebase(URL);
// listen for all changes and update
fb.endAt().limit(100).on('value', update);
// print the output of our array
function update(snap) {
var list = [];
snap.forEach(function(ss) {
var data = ss.val();
data['.priority'] = ss.getPriority();
data['.name'] = ss.name();
list.unshift(data);
});
// print/process the results...
}
Note that this is quite performant even up to perhaps a thousand records (assuming the payloads are small). For more robust usages, Frank's answer is authoritative and much more scalable.
This brute force can also be optimized to work with bigger data or more records by doing things like monitoring child_added/child_removed/child_moved events in lieu of value, and using a debounce to apply DOM updates in bulk instead of individually.
DOM updates, naturally, are a stinker regardless of the approach, once you get into the hundreds of elements, so the debounce approach (or a React.js solution, which is essentially an uber debounce) is a great tool to have.
There is really no way but seems we have the recyclerview we can have this
query=mCommentsReference.orderByChild("date_added");
query.keepSynced(true);
// Initialize Views
mRecyclerView = (RecyclerView) view.findViewById(R.id.recyclerView);
mManager = new LinearLayoutManager(getContext());
// mManager.setReverseLayout(false);
mManager.setReverseLayout(true);
mManager.setStackFromEnd(true);
mRecyclerView.setHasFixedSize(true);
mRecyclerView.setLayoutManager(mManager);
I have a date variable (long) and wanted to keep the newest items on top of the list. So what I did was:
Add a new long field 'dateInverse'
Add a new method called 'getDateInverse', which just returns: Long.MAX_VALUE - date;
Create my query with: .orderByChild("dateInverse")
Presto! :p
You are searching limitTolast(Int x) .This will give you the last "x" higher elements of your database (they are in ascending order) but they are the "x" higher elements
if you got in your database {10,300,150,240,2,24,220}
this method:
myFirebaseRef.orderByChild("highScore").limitToLast(4)
will retrive you : {150,220,240,300}
In Android there is a way to actually reverse the data in an Arraylist of objects through the Adapter. In my case I could not use the LayoutManager to reverse the results in descending order since I was using a horizontal Recyclerview to display the data. Setting the following parameters to the recyclerview messed up my UI experience:
llManager.setReverseLayout(true);
llManager.setStackFromEnd(true);
The only working way I found around this was through the BindViewHolder method of the RecyclerView adapter:
#Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
final SuperPost superPost = superList.get(getItemCount() - position - 1);
}
Hope this answer will help all the devs out there who are struggling with this issue in Firebase.
Firebase: How to display a thread of items in reverse order with a limit for each request and an indicator for a "load more" button.
This will get the last 10 items of the list
FBRef.child("childName")
.limitToLast(loadMoreLimit) // loadMoreLimit = 10 for example
This will get the last 10 items. Grab the id of the last record in the list and save for the load more functionality. Next, convert the collection of objects into and an array and do a list.reverse().
LOAD MORE Functionality: The next call will do two things, it will get the next sequence of list items based on the reference id from the first request and give you an indicator if you need to display the "load more" button.
this.FBRef
.child("childName")
.endAt(null, lastThreadId) // Get this from the previous step
.limitToLast(loadMoreLimit+2)
You will need to strip the first and last item of this object collection. The first item is the reference to get this list. The last item is an indicator for the show more button.
I have a bunch of other logic that will keep everything clean. You will need to add this code only for the load more functionality.
list = snapObjectAsArray; // The list is an array from snapObject
lastItemId = key; // get the first key of the list
if (list.length < loadMoreLimit+1) {
lastItemId = false;
}
if (list.length > loadMoreLimit+1) {
list.pop();
}
if (list.length > loadMoreLimit) {
list.shift();
}
// Return the list.reverse() and lastItemId
// If lastItemId is an ID, it will be used for the next reference and a flag to show the "load more" button.
}
I'm using ReactFire for easy Firebase integration.
Basically, it helps me storing the datas into the component state, as an array. Then, all I have to use is the reverse() function (read more)
Here is how I achieve this :
import React, { Component, PropTypes } from 'react';
import ReactMixin from 'react-mixin';
import ReactFireMixin from 'reactfire';
import Firebase from '../../../utils/firebaseUtils'; // Firebase.initializeApp(config);
#ReactMixin.decorate(ReactFireMixin)
export default class Add extends Component {
constructor(args) {
super(args);
this.state = {
articles: []
};
}
componentWillMount() {
let ref = Firebase.database().ref('articles').orderByChild('insertDate').limitToLast(10);
this.bindAsArray(ref, 'articles'); // bind retrieved data to this.state.articles
}
render() {
return (
<div>
{
this.state.articles.reverse().map(function(article) {
return <div>{article.title}</div>
})
}
</div>
);
}
}
There is a better way. You should order by negative server timestamp. How to get negative server timestamp even offline? There is an hidden field which helps. Related snippet from documentation:
var offsetRef = new Firebase("https://<YOUR-FIREBASE-APP>.firebaseio.com/.info/serverTimeOffset");
offsetRef.on("value", function(snap) {
var offset = snap.val();
var estimatedServerTimeMs = new Date().getTime() + offset;
});
To add to Dave Vávra's answer, I use a negative timestamp as my sort_key like so
Setting
const timestamp = new Date().getTime();
const data = {
name: 'John Doe',
city: 'New York',
sort_key: timestamp * -1 // Gets the negative value of the timestamp
}
Getting
const ref = firebase.database().ref('business-images').child(id);
const query = ref.orderByChild('sort_key');
return $firebaseArray(query); // AngularFire function
This fetches all objects from newest to oldest. You can also $indexOn the sortKey to make it run even faster
I had this problem too, I found a very simple solution to this that doesn't involved manipulating the data in anyway. If you are rending the result to the DOM, in a list of some sort. You can use flexbox and setup a class to reverse the elements in their container.
.reverse {
display: flex;
flex-direction: column-reverse;
}
myarray.reverse(); or this.myitems = items.map(item => item).reverse();
I did this by prepend.
query.orderByChild('sell').limitToLast(4).on("value", function(snapshot){
snapshot.forEach(function (childSnapshot) {
// PREPEND
});
});
Someone has pointed out that there are 2 ways to do this:
Manipulate the data client-side
Make a query that will order the data
The easiest way that I have found to do this is to use option 1, but through a LinkedList. I just append each of the objects to the front of the stack. It is flexible enough to still allow the list to be used in a ListView or RecyclerView. This way even though they come in order oldest to newest, you can still view, or retrieve, newest to oldest.
You can add a column named orderColumn where you save time as
Long refrenceTime = "large future time";
Long currentTime = "currentTime";
Long order = refrenceTime - currentTime;
now save Long order in column named orderColumn and when you retrieve data
as orderBy(orderColumn) you will get what you need.
just use reverse() on the array , suppose if you are storing the values to an array items[] then do a this.items.reverse()
ref.subscribe(snapshots => {
this.loading.dismiss();
this.items = [];
snapshots.forEach(snapshot => {
this.items.push(snapshot);
});
**this.items.reverse();**
},
For me it was limitToLast that worked. I also found out that limitLast is NOT a function:)
const query = messagesRef.orderBy('createdAt', 'asc').limitToLast(25);
The above is what worked for me.
PRINT in reverse order
Let's think outside the box... If your information will be printed directly into user's screen (without any content that needs to be modified in a consecutive order, like a sum or something), simply print from bottom to top.
So, instead of inserting each new block of content to the end of the print space (A += B), add that block to the beginning (A = B+A).
If you'll include the elements as a consecutive ordered list, the DOM can put the numbers for you if you insert each element as a List Item (<li>) inside an Ordered Lists (<ol>).
This way you save space from your database, avoiding unnecesary reversed data.
In my android project i am working on adding a pull to refresh, Since there is nothing mentioned in the document,where i can add pull to refresh directly i have used android SwipeRefreshLayout and developed a pull to refresh functionality. For that to success i need to get latest data set onRefresh() method. So i have saved the last shown ParseObject "createdAt" time as getLastPostDate() and tried to query latest data from last time up to now every time user pulls to refresh as like below query.
query.whereGreaterThanOrEqualTo("createdAt", getLastPostDate());
postList = query.find();
But for some reason i can't query from "createdAt" or "updatedAt" value. Help is appreciated.
EDIT
#JayDev here how i did it.
final ParseQuery<Post> query = Post.getQuery();
query.orderByDescending("createdAt");
postList = query.find(); // getting all the posts
setLastPostDate(postList.get(0).getCreatedAt()); // set the last post date
since posts are in descending order , get i can get the last post from 0 element. (This works!!)
on refresh i use the above code, to get latest posts posted after that date. Please guide me if there is another way to