Hi i have a noSql db in firebase.
I want to get the object where userId is 288
i'v tried many combinations but i cant figure out how its done.
This is my code so far :
var refTest= database.ref('conversation')
var query = refTest
.orderByChild('messages');
query.on('value', function(data) {
var a = data.val();
console.log(a.messages.userId);
console.log(data.val());
});
This is a image of my "schema"
I'm obviously a noob when it comes to NoSQL. I do understand SQL
All help is appreciated
You can order/filter on a nested value like this:
var refTest= database.ref('conversation')
var query = refTest.orderByChild('messages/userId').equalTo("288");
query.on('value', function(snapshot) {
snapshot.forEach(function(child) {
console.log(child.key);
console.log(child.val());
});
});
The forEach is needed, since there may be multiple child nodes with messages/userId equal to 288.
The key named "messages" doesn't make sense in your schema. Because if you want to have another message under that conversation, then you wouldn't be able to add it with the same key name and you also couldn't add it under "messages" because it would overwrite the other one. My suggestion is to use the push() method for adding a new message. This way you uniquely identify each message.
Regarding your question, an easy to understand way of parsing your schema is this: you loop through each message of each conversation for finding the messages with userID.
refTest.on('value', function(data) {
var conversations = data.val();
for (conversation in conversations){
for (message in conversation) {
if (message.userId == 288) {
// do whatever you need
// and eventually return something to break the loops
}
}
}
}
Of course, you can adapt it based on your needs
Given
var messageListRef = new Firebase('https://SampleChat.firebaseIO-demo.com/message_list');
messageListRef.push({ 'user_id': 'fred', 'text': 'Yabba Dabba Doo!' });
How to remove that added data { 'user_id': 'fred', 'text': 'Yabba Dabba Doo!' } later from Firebase? Is there a clean and simple way to do that?
I would like to be able to find that data again later and then remove it, assuming I don't know the unique id generated, I can't do new Firebase('https://SampleChat.firebaseIO-demo.com/message_list/'+uniqueId).remove() (and I don't know if this is the good practice). In my idea I would first query the data but I don't know how I can do that with a list of data. For example, I would like to be able to remove that data onDisconnect.
On that page https://www.firebase.com/docs/web/api/firebase/push.html, it seems the "See Lists of Data" is not yet written. Is it in the roadmap to add such remove for lists of data?
When you call push it returns the new node. So you could keep a list of messages the user added in memory:
var myMessageKeys = []; // put this somewhere "globally"
And then whenever you add a message:
var newMessageRef = messageListRef.push({ 'user_id': 'fred', 'text': 'Yabba Dabba Doo!' });
myMessageKeys.push(newMessageRef.key());
Personally this feels hacky to me. I would prefer to use a query, so that for example if fred disconnects you'd do something like:
var myMessages = messageListRef.orderByChild('user_id').equalTo('fred');
myMessages.on('value', function(messagesSnapshot) {
messagesSnapshot.forEach(function(messageSnapshot) {
messageSnapshot.ref().remove();
});
});
So figuring out which messages to remove is the trick. But suppose you want to delete by user id; perhaps when Fred disconnects, you want to remove all of his messages. You could find and delete them like this:
var query = messageListRef.orderByChild('user_id').equalTo('Fred');
query.once('child_added', function(snapshot) {
snapshot.forEach( function(msg) {
msg.ref().remove();
});
});
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 client UI I have a form with differents search criterias, and I'd like to reactively update the results list. The search query is transformed into a classical minimongo selector, saved in a Session variable, and then I have observers to do things with the results:
// Think of a AirBnb-like application
// The session variable `search-query` is updated via a form
// example: Session.set('search-query', {price: {$lt: 100}});
Offers = new Meteor.Collection('offers');
Session.setDefault('search-query', {});
resultsCursor = Offers.find(Session.get('search-query'));
// I want to add and remove pins on a map
resultCursor.observe({
added: Map.addPin,
removed: Map.removePin
});
Deps.autorun(function() {
// I want to modify the cursor selector and keep the observers
// so that I would only have the diff between the old search and
// the new one
// This `modifySelector` method doesn't exist
resultsCursor.modifySelector(Session.get('search-query'));
});
How could I implement this modifySelector method on the cursor object?
Basically I think this method needs to update the compiled version of the cursor, ie the selector_f attribute, and then rerun observers (without losing the cache of the previous results). Or is there any better solution?
Edit: Some of you have misunderstood what I'm trying to do. Let me provide a complete example:
Offers = new Meteor.Collection('offers');
if (Meteor.isServer && Offers.find().count() === 0) {
for (var i = 1; i < 4; i++) {
// Inserting documents {price: 1}, {price: 2} and {price: 3}
Offers.insert({price:i})
}
}
if (Meteor.isClient) {
Session.setDefault('search-query', {price:1});
resultsCursor = Offers.find(Session.get('search-query'));
resultsCursor.observe({
added: function (doc) {
// First, this added observer is fired once with the document
// matching the default query {price: 1}
console.log('added:', doc);
}
});
setTimeout(function() {
console.log('new search query');
// Then one second later, I'd like to have my "added observer" fired
// twice with docs {price: 2} and {price: 3}.
Session.set('search-query', {});
}, 1000);
}
This doesn't solve the problem in the way you seem to be wanting to, but I think the result is still the same. If this is a solution you explicitly don't want, let me know and I can remove the answer. I just didn't want to put code in a comment.
Offers = new Meteor.Collection('offers');
Session.setDefault('search-query', {});
Template.map.pins = function() {
return Offers.find(Session.get('search-query'));
}
Template.map.placepins = function(pins) {
// use d3 or whatever to clear the map and then place all pins on the map
}
Assuming your template is something like this:
<template name="map">
{{placepins pins}}
</template>
One solution is to manually diff the old and the new cursors:
# Every time the query change, do a diff to add, move and remove pins on the screen
# Assuming that the pins order are always the same, this use a single loop of complexity
# o(n) rather than the naive loop in loop of complexity o(n^2)
Deps.autorun =>
old_pins = #pins
new_pins = []
position = 0
old_pin = undefined # This variable needs to be in the Deps.autorun scope
# This is a simple algo to implement a kind of "reactive cursor"
# Sorting is done on the server, it's important to keep the order
collection.find(Session.get('search-query'), sort: [['mark', 'desc']]).forEach (product) =>
if not old_pin?
old_pin = old_pins.shift()
while old_pin?.mark > product.mark
#removePin(old_pin)
old_pin = old_pins.shift()
if old_pin?._id == product._id
#movePin(old_pin, position++)
new_pins.push(old_pin)
old_pin = old_pins.shift()
else
newPin = #render(product, position++)
new_pins.push(newPin)
# Finish the job
if old_pin?
#removePin(old_pin)
for old_pin in old_pins
#removePin(old_pin)
#pins = new_pins
But it's a bit hacky and not so efficient. Moreover the diff logic is already implemented in minimongo so it's better to reuse it.
Perhaps an acceptable solution would be to keep track of old pins in a local collection? Something like this:
Session.setDefault('search-query', {});
var Offers = new Meteor.Collection('offers');
var OldOffers = new Meteor.Collection(null);
var addNewPin = function(offer) {
// Add a pin only if it's a new offer, and then mark it as an old offer
if (!OldOffers.findOne({_id: offer._id})) {
Map.addPin(offer);
OldOffers.insert(offer);
}
};
var removePinsExcept = function(ids) {
// Clean out the pins that no longer exist in the updated query,
// and remove them from the OldOffers collection
OldOffers.find({_id: {$nin: ids}}).forEach(function(offer) {
Map.removePin(offer);
OldOffers.remove({_id: offer._id});
});
};
Deps.autorun(function() {
var offers = Offers.find(Session.get('search-query'));
removePinsExcept(offers.map(function(offer) {
return offer._id;
}));
offers.observe({
added: addNewPin,
removed: Map.removePin
});
});
I'm not sure how much faster this is than your array answer, though I think it's much more readable. The thing you need to consider is whether diffing the results as the query changes is really much faster than removing all the pins and redrawing them each time. I would suspect that this might be a case of premature optimization. How often do you expect a user to change the search query, such that there will be a significant amount of overlap between the results of the old and new queries?
I have the same problem in my own hobby Meteor project.
There is filter session var where selector is storing. Triggering any checkbox or button changes filter and all UI rerender.
That solution have some cons and the main - you can't share app state with other users.
So i realized that better way is storing app state in URL.
May be it is also better in your case?
Clicking button now change URL and UI rendering based on it. I realize it with FlowRouter.
Helpful reading: Keeping App State on the URL
I'm making a simple app that informs a client that other clients clicked a button. I'm storing the clicks in a Firebase (db) using:
db.push({msg:data});
All clients get notified of other user's clicks with an on, such as
db.on('child_added',function(snapshot) {
var msg = snapshot.val().msg;
});
However, when the page first loads I want to discard any existing data on the stack. My strategy is to call db.once() before I define the db.on('child_added',...) in order to get the initial number of children, and then use that to discard that number of calls to db.on('child_added',...).
Unfortunately, though, all of the calls to db.on('child_added',...) are happening before I'm able to get the initial count, so it fails.
How can I effectively and simply discard the initial data?
For larger data sets, Firebase now offers (as of 2.0) some query methods that can make this simpler.
If we add a timestamp field on each record, we can construct a query that only looks at new values. Consider this contrived data:
{
"messages": {
"$messageid": {
"sender": "kato",
"message": "hello world"
"created": 123456 // Firebase.ServerValue.TIMESTAMP
}
}
}
We could find messages only after "now" using something like this:
var ref = new Firebase('https://<your instance>.firebaseio.com/messages');
var queryRef = ref.orderBy('created').startAt(Firebase.ServerValue.TIMESTAMP);
queryRef.on('child_added', function(snap) {
console.log(snap.val());
});
If I understand your question correctly, it sounds like you only want data that has been added since the user visited the page. In Firebase, the behavior you describe is by design, as the data is always changing and there isn't a notion of "old" data vs "new" data.
However, if you only want to display data added after the page has loaded, try ignoring all events prior until the complete set of children has loaded at least once. For example:
var ignoreItems = true;
var ref = new Firebase('https://<your-Firebase>.firebaseio.com');
ref.on('child_added', function(snapshot) {
if (!ignoreItems) {
var msg = snapshot.val().msg;
// do something here
}
});
ref.once('value', function(snapshot) {
ignoreItems = false;
});
The alternative to this approach would be to write your new items with a priority as well, where the priority is Firebase.ServerValue.TIMESTAMP (the current server time), and then use a .startAt(...) query using the current timestamp. However, this is more complex than the approach described above.