I'm attempting to perform a complex query with firestore v9. My intention is to get some docs (skip and limit) from a my data structure. What I mean is, I need to get for example 5 docs from a doc -> collections -> doc. and this docs need to be order by there date.
So for example, lets say in my array I contain 2 docs id ['e4z3HNyUCQbiYQRzfVO4RyebMCP2', 'WZImI6tl0IUFKbICEZzcciaUxKG2'], from this 2 docs, I would need to get their userPosts ordered by the creation date, but I would need to pass a skip and limit too. So from this 2 docs, I would limit 3 docs to get, but these 3 docs will be from the 2 posts ids I passed.
const queryBuild = await query(
collection(db, 'posts'),
where('userPosts', 'in', [`post.id`...]),
collection(db, 'userPosts'),
...
);
const querySnapshot = await getDocs(queryBuild);
There is no out-of-the-box way to do what you are looking for with Firestore.
You will need to issue two queries, one for each of the two parent document.
Let say, for example, that in total you only want 3 documents from the two sub-collections.
You first query the first subcollection with the following query:
const q1 = query(collection(db, "posts/e4z3HNyUCQbiYQRzfVO4RyebMCP2/userPosts"), orderBy("creation", "desc"), limit(3));
You then query the second subcollection with the following query:
const q2 = query(collection(db, "posts/WZImI6tl0IUFKbICEZzcciaUxKG2/userPosts"), orderBy("creation", "desc"), limit(3));
Then you merge the two results (i.e. push the documents of the two QuerySnapshots in one Array), order them by descending creation value and take the first three ones.
An alternative to Renaud's answer would be to store the postId of the parent document in each userPost. With that you could add an in clause to a collection group query to get the user posts of up to 10 parent documents.
query(
collectionGroup(db, "userPosts"),
orderBy("creation", "desc"),
where("parentPostId", "in", ["e4z3HNyUCQbiYQRzfVO4RyebMCP2", "WZImI6tl0IUFKbICEZzcciaUxKG2"]),
limit(3)
);
If you have more than 10 IDs, you'll need to perform multiple of such queries, so you'd be back to a similar approach as in Renaud answers, just with 1/10th as many API calls.
I have been trying to search for a way to do pagination for Firebase Realtime Database. I see a lot of tutorial/articles on pagination for Cloud Firestore but nothing for Realtime Database. Below is my code and its working as expected. Can anyone point me in the right direction for adding pagination to this? If even possible? Any help would be appreciated.
const [ufoSightings, setUfoSightings] = useState([]);
const [userStateSelection, setUserStateSelection] = useState("");
useEffect(() => {
let allUfo = [];
//referencing firebase db
const ufoRef = firebase.database().ref("ufos");
//filter database searching for specific state user is looking for
const query = ufoRef
.orderByChild("state")
.equalTo(`${userStateSelection}`)
.limitToFirst(12);
query.once("value").then((snapshot) => {
//storing ufoSightings in state
snapshot.forEach((snap) => {
allUfo.push(snap.val());
});
setUfoSightings(allUfo);
});
}, [userStateSelection]);
when I tried Frank van Puffelen's answer to query for the next page, I got an error that says
Error: startAfter: Starting point was already set (by another call to startAt, startAfter, or equalTo).
After going through this firebase documentation here is a query that worked for me to get next page
const query = ufoRef.orderByChild("state")
.startAt(`${userStateSelection}`,lastKey)
.endAt(`${userStateSelection}`).limitToFirst(12)
.once("value");
The only drawback is lastKey's list value will be fetched every time you query for the next page which is redundant, so you have to take care of that.
The reason why it worked for me:
From this firebase documentation
startAt ( value : number | string | boolean | null , key ? : string ) : Query
The starting point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name greater than or equal to the specified key.
endAt ( value : number | string | boolean | null , key ? : string ) : Query
The ending point is inclusive, so children with exactly the specified value will be included in the query. The optional key argument can be used to further limit the range of the query. If it is specified, then children that have exactly the specified value must also have a key name less than or equal to the specified key.
So the query will try to fetch
state >= userStateSelection && state <= userStateSelection (lexicographically)
which will equal to
state == userStateSelection
To get the next page, you pass in the state and key of the node to start at or after
So say you capture the values in your listener with this:
var lastState, lastKey;
query.once("value").then((snapshot) => {
//storing ufoSightings in state
snapshot.forEach((snap) => {
allUfo.push(snap.val());
lastState = snap.val().state; // 👈
lastKey = snap.key; // 👈
});
setUfoSightings(allUfo);
});
Now you can get the next page with this query:
const query = ufoRef
.orderByChild("state")
.equalTo(`${userStateSelection}`)
.startAfter(lastState, lastKey) // 👈
.limitToFirst(12);
The startAfter() method is relatively new to the Realtime Database, so if you can't find it or are having trouble with it try the (much older) startAt() method with the same arguments.
Also check out some of the many other questions on firebase-realtime-database pagination, as this has been covered here quite frequently already.
I am trying to pull a URL for an image in storage that is currently logged in the firebase real time database.
This is for a game of snap - there will be two cards on the screen (left image and right image) and when the two matches the user will click snap.
All of my image urls are stored in the following way:
Each one has a unique child called "index" - I also have another tree that is just a running count of each image record. So currently I am running a function that checks the total of the current count, then performs a random function to generate a random number, then performs a database query on the images tree using orderByChild and an equalTo that contains the random index number.
If I log the datasnap of this I can see a full node for one record (So index, score, url, user and their values) however if I try to just pull the URL I get returned a value of Null. I can, rather annoyingly, return the term "URL" seemingly at my leisure but I can't get the underlying value. I've wondered if this is due to it being a string and not a numeric but I can't find anything to suggest that is a problem.
Please bare in mind I've only been learning Javascript for about a week at max, so if I'm making obvious rookie errors that's probably why!
Below is a code snippet to show you what I mean:
var indRef = firebase.database().ref('index')
var imgRef = firebase.database().ref('images')
var leftImg = document.getElementById('leftImg')
var rightImg = document.getElementById('rightImg')
document.addEventListener('DOMContentLoaded', function(){
indRef.once('value')
.then(function(snapShot){
var indMax = snapShot.val()
return indMax;
})
.then(function(indMax){
var leftInd = Math.floor(Math.random()* indMax + 1)
imgRef.orderByChild('index').equalTo(leftInd).once('value', function(imageSnap){
var image = imageSnap.child('url').val();
leftImg.src=image;
})
})
})
When you execute a query against the Firebase Database, there will potentially be multiple results. So the snapshot contains a list of those results. Even if there is only a single result, the snapshot will contain a list of one result.
Your code needs to cater for that list, by looping over Snapshot.forEach():
imgRef.orderByChild('index').equalTo(leftInd).once('value', function(imageSnap){
imageSnap.forEach(function(child) {
var image = child.child('url').val();
leftImg.src=image;
})
})
I'm building an API for my site (using Node.js and Mongoose) and I would like to incorporate pagination in it. My problem is the following: if the page size is for example 15 and I make a request for the first page so it sends me the first 15 items ordered by date of creation but then what if before I make the request for the second page, 15 new items are created in the database, the returned data will be the same as previously if I just use a skip on mongoose.
Is there a way to avoid doublons with mongoose? What I have at the moment is an "exclude" parameter in the query so it excludes all items already loaded but I'm thinking if there are lots of loaded items, the URL might be very long and I'm not sure that's a good thing...
Is there a better way to do this or do I have to just leave it with the risk of having doublons?
You can use mongoose-paginate-v2
And to prevent any duplicates from returned documents, you can pass (last document id & limit)
And your query should be like :
import { PaginateModel } from 'mongoose-paginate-v2';
constructor(
private readonly _paginateModel: PaginateModel<any>
) {}
const query = this._paginateModel
.find({ _id: { $lt: lastId } });
this._paginateModel.paginate(query, { limit: 10 });
You can use skip and limit function in which you can pass min and max value .
like in first page if you get 15 records values for min and max will be :
min = 0 and max = 15
for page 2
min = 15 and max = 30
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.