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.
Related
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;
})
})
This is the JSON I'm working with:
https://data.cityofnewyork.us/resource/xx67-kt59.json?$where=camis%20=%2230112340%22
I'd be dynamically making the queries using different data, so it'll possibly change.
What I'm essentially trying to do is to somehow organize the elements within this array into different arrays based on inspection_date.
So for each unique inspection_date value, those respective inspections would be put into its own collection.
If I knew the dates beforehand, I could easily iterate through each element and just push into an array.
Is there a way to dynamically create the arrays?
My end goal is to be able to display each group of inspections (based on inspection date) using Angular 5 on a webpage. I already have the site up and working and all of the requests being made.
So, I'm trying to eventually get to something like this. But of course, using whatever dates in the response from the request.
2016-10-03T00:00:00
List the inspections
2016-04-30T00:00:00
List the inspections
2016-04-12T00:00:00
List the inspections
Just for reference, here's the code I'm using:
ngOnInit() {
this.route.params.subscribe(params => {
this.title = +params['camis']; // (+) converts string 'id' to a number
this.q.getInpectionsPerCamis(this.title).subscribe((res) => {
this.inspectionList = res;
console.log(res);
});
// In a real app: dispatch action to load the details here.
});
}
I wish I could give you more info, but at this point, I'm just trying to get started.
I wrote this in jQuery just because it was faster for me, but it should translate fairly well to Angular (I just don't want to fiddle with an angular app right now)
Let me know if you have any questions.
$(function() {
let byDateObj = {};
$.ajax({
url: 'https://data.cityofnewyork.us/resource/xx67-kt59.json?$where=camis%20=%2230112340%22'
}).then(function(data) {
//probably do a check to make sure the data is an array, im gonna skip that
byDateObj = data.reduce(function(cum, cur) {
if (!cum.hasOwnProperty(cur.inspection_date)) cum[cur.inspection_date] = [];
//if the cumulative array doesn't have the inspection property already, add it as an empty array
cum[cur.inspection_date].push(cur);
//push to inspection_date array.
return cum;
//return cumulatie object
}, byDateObj);
//start with an empty object by default;
console.log(byDateObj);
}, console.error);
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
I am trying to solve a problem I am seeing when rendering a list of items in my ui that is coming out of a es6 class I have created. The model is working great, however I am using animations that are listening to (in react) mount, onEnter, and onLeave of the items.
When I apply my filters and sorting via the model and spit back the new list of items via the getter, the animations do not apply to some items because the list is just being re sorted, not necessarily changed.
So my getter just grabs this.products of the class and returns it and applies a sort order to it. And if filters are applied (which are tracked by this._checkedList in the class), the this.products is reduced based on which filters are selected then sorted. So that getter looks like so :
get productList() {
if (this._checkedList.length > 0) {
const filteredProducts = _.reduce(this.filterMap, reduceFilters, []);
const deDuped = _.uniq(filteredProducts, 'id');
return this.applySort(deDuped);
}
const deDuped = _.uniq(this.products, 'id');
return this.applySort(deDuped);
}
What I am trying to figure out, is a way to to temporarily send back an empty array while the filters or sorting run. The reason being the ui would receive an empty array (even if for a split second) and react would register the new sorted/filtered list as a new list and fire the enter/leave/mount animations again.
My attempt was to set a local property of the class like -
this._tempReturn = false;
then in the functions where the sort or filter happen, I set it to true, then back to false when the function is done like this -
toggleFilter(args) {
this._tempReturn = true;
...toggle logic
this._tempReturn = false;
}
Then changed the getter to check for that property before i do anything else, and if it's true, send back an empty array -
get productList() {
if (this._tempReturn) {
return [];
}
...
}
However, this does not seem to work. Even putting a console.log in the if (this._tempReturn) { didn't show any logs.
I also tried sending back a new list with lodash's _.cloneDeep like so :
get productList() {
if (this._checkedList.length > 0) {
const filteredProducts = _.reduce(this.filterMap, reduceFilters, []);
const deDuped = _.uniq(filteredProducts, 'id');
return _.cloneDeep(this.applySort(deDuped));
}
const deDuped = _.uniq(this.products, 'id');
return _.cloneDeep(this.applySort(deDuped));
}
this did not work either. So it seems the empty array return might be a better approach.
I am wondering if there is some way to achieve this - I would like to have the array be return empty for a second perhaps while the filters and sort are applying.
Very stuck on how to achieve, perhaps I am even looking at this problem from the wrong angle and there is a much better way to solve this. Any advice would be welcomed, thanks for reading!
In order to force a re-render of items in a list when updating them you just need to make sure that each items has a unique key property.
Instead of rendering the list, then rendering it as empty, then re-rendering a changed list make sure each child has a unique key. Changing the key property on a child in an array will always cause it to re-render.
I'm relatively new to NoSQL, but I have been enjoying the journey very much! I am however finding the map-reduce way of life a bit tricky! I need some help with a problem!
I have a database with two types of documents, opening transactions and closing transactions. For replication and offline functionality reasons I cannot merge the data into one document. The opening transaction document looks something like :
{
_id: "transaction-open-randomgeneratedstring",
type: "transactions-open",
vehicle: "vehicle-id",
created: "date string"
}
The closing documents looks something like:
{
_id: "transaction-close-randomgeneratedstring",
type: "transactions-close",
openid: "transaction-open-randomgeneratedstring",
created: "date string"
}
The randomgeneratedstring of a closing transactions match the randomgeneratedstring of the corresponding opening transaction.
I need a map-reduce to give me the list of open transactions that does not have a corresponding closing transaction. This will basically give me a list of outstanding transactions.
This is the map-reduce I have thus far, but it is not doing the job.
{
"map": function(doc) {
if(doc.type == "transactions-open") {
emit([doc._id, 0], "OPEN");
}
if(doc.type == "transactions-close"){
emit([doc.openid, 1], "CLOSE");
}
},
"reduce": function(keys, values, rereduce) {
var unique_labels = {};
var open = {};
keys.forEach(function(label) {
if(!unique_labels[label[0]]) {
unique_labels[label[0]] = true;
} else {
open[label[0]] = true;
}
});
return open;
}
}
I am open for changes in the _id naming / structure, but I cannot combine the two documents into one.
Thanks!
EDIT
Based on response from Hod, I changed the reduce to look like:
function(keys, values, rereducer)
{
if(values.length == 1)
return true;
}
This is certainly a step in the right direction, but the unwanted transactions are still in the result set, the value is only null. Is there no way to get those out of the result set?
As described - what you would do with a Join in SQL you do with a reduce in CouchDB. Code something like this - not tested:
{
"map": function(doc) {
if(doc.type == "transactions-open") {
emit([doc._id], 1);
}
if(doc.type == "transactions-close"){
emit([doc.openid], -1);
}
},
"reduce": "_sum";
}
So we emit a 1 for an open transaction under an ID and a -1 for a close under the same ID. Now when you reduce you will get a result for each ID of:
-1 = Closed with no record of an open (error condition).
0 = Opened and Closed
1 = Open and not yet closed.
The problem is with the keys parameter in your reduce function. The reduce phase is not called once with all possible keys. It's called per distinct key, and based on the group_level you specify.
Looking at your code, if you haven't specified any group_level, your reduce function is going to get called for every document separately.
Because you're emitting the id of the open transaction doc for both open and close markers, if you grouped at the first level, you'd get open or open/close pairs. You're still only getting a reduction on a limited set of docs at a time.
You could fix this either in your logic calling the query, or by emitting a key that let's you reduce on the entire set at once. (I imagine there are other ways too. These are the ones that come to mind.)
If you use the key approach, you'd need to emit something that looked like ["transaction", doc._id, 0]. Then a first level grouping would give you the whole transaction set like you're current code expects.
EDIT (Adding information based on edit of question.)
The reduce function is going to get called with whatever grouping you set up. It's always going to return something, even if it's just no results emitted (i.e. null).
If you don't want to handle that in the logic that's running the queries and processing the results, you need to use an approach that will allow you to group all the transaction documents together, instead of just the documents for a single transaction.
Based on what you've done so far, another approach would be to forgo the reduce phase and just look at the number of results returned by a query that's limited to the unique doc id.
I have a problem, I seeked help in #documentcloud on Freenode and got some suggestions but still hasn't helped me fix my problem.
Basically I have a collection, very large up to 2-3 thousand items, and it -has- to be sorted, however it only has to be sorted at certain times. Using a comparator function is fine, it keeps it sorted, but takes a lot longer when all the items are being added to the collection, as it's resorting the entire collection each time one of the 2-3000 items are added.
I've tried a couple of suggestions, one being:
collection.comparator = function(object) { object.get('sortBy'); };
collection.sort();
collection.comparator = undefined;
This fails miserably and doesn't sort at all, I've also tried using collection.sortBy(...) this seems to return the sorted collection, but it is of no use to me as when I try collection = collection.sortBy(...) it just dumps the sorted collection as an array into the variable collection. When I try to use collection functions or utilities I get errors like .each is undefined for collection, etc.
Any ideas?
This can't be done simply because Collection.sort actually calls Collection.comparator.
You have basically three options
Option One
You could force your sort method without comparator to the models itself ( basically the same as calling .sort of your collection, but without .comparator
// in your collection class
_comparator: function(a,b) { /* comparator code */ }
sorter: function() {
// Of course you should bind this to your collection at this function
// and your comparator
this.models.sort( _comparator ) // .models gives you the array of all models
}
Option Two
Remove comparator each time you add something to the collection
_comparator = function(a,b) { /* comparator code */ }
collection.comparator = undefined
collection.fetch({ success: function() { collection.comparator = _comparator })
Options Three
If you think a little bit ahead of your code, and simply want your collection sorted only because you want to display it this way, you could simply sort it on display
collection.returnSorted = function () { return collection.sortBy( _comparator ) }
Try this:
collection.add(model, {sort: false});
Would it work to use _.sortedIndex() when individual items are added to the already sorted list?
You could easily figure out the sortedIndex, slice the list based on that index, then splice: part1 + new_entry + part2.
This keeps you from sorting the entire list every time. You're just inserting one new entry in the right spot.
My answer assumes you're already able to do an initial sort of the 2000+ item collection, and that you're just trying to overcome the issue of resort when new items are added one at a time. Your question lacks specificity about exactly where your issue is though.