I want to return a $firebaseArray of records that contain a particular value without knowing the parent ID.
So in this case, I want to get all the objects under 'challenges' that contain the ID pictured above starting with LNF.
I have tried using orderByChild and equalTo, but again this seems to requiring knowing the parent ID. Is there a way around this?
If you want everything with key CPjip3tVE1Q067Qzx6p0vij0k1|1try this:
var key = "CPjip3tVE1Q067Qzx6p0vij0k1|1";
for child in snapshot.children {
if child.key == key {
get your data
}
}
You can use that to loop over all of the children under "challenges"
As a scenario, the user can click a button to create a list of timestamps that shows the corresponding times when the clicks are made. User can also click on an item on the list to remove an item.
In terms of the store, there's a counter state that keeps track of how many times the button has been clicked, and then there's another state that keeps track of a list of timestamps. And each item on list state has an id field that derive from the counter state. So one part of the store depends on another part.
As an attempt, I dispatch one action, and both reducers handle the same action, and it works fine, but only that it's not DRY. Before dispatching, I have to add 1 to the counter state in order to get the new id which I use as the action payload, after dispatching, I add 1 to the counter state again to return the new counter state. That's repeating myself.
What's the general standard way of handling a problem of this nature?
The general simple way is to use thunks. You need to setup a middleware, check out the docs:
https://github.com/gaearon/redux-thunk
This allows you to dispatch a function instead of a simple action. Within that function, you can access state and dispatch as many times as you want.
In your scenario, you would first increment the counter, then retrieve the length to get your new id, and then dispatch another action to create a timestamp.
Some imaginary code for your action creators:
// basic action creators to be handled in your reducers
function incrementCounter(){
return { type: 'INCREMENT'}
}
function createTimestamp(id){
return { type: 'CREATE_TS', id }
}
// this is the thunk
function incrementAndTimestamp(){
return (dispatch, getState) => {
// increment the counter
dispatch(incrementCounter())
// generate an "id" from the resulting state
const newId = getState().counter.length
// and use that id to further update your state
dispatch(createTimestamp(newId))
}
}
You will need to handle those 2 different actions in your reducers and you have now two separate pieces of code. The thunk is the glue that dispatches, gets the data from one part, and uses it to affect the other part.
thanks for reading and helping. Here is my situation so far:
I have much data in database, each piece of data has id, parentid(which means you can find the id of its parent using this parentid ), name, description.
I want to create a dynamic tree using react,but I do not know how many levels of nodes I have. Each node represents for an id in database. An user clicks on a node A on this tree, the children nodes whose parentid equals to A's id will show/hide.
I do not intend to retrieve all the data because it will take long time. Now I am able to get one node's children by sending request and get response.body:
getChildren(id){
ajax.get('http://localhost:8080/configmgmt/code/category/retriveTree/' + id)
.end((error, response) => {
if (!error && response) {
console.dir(response.body );
this.setState(subdata:response.body});
} else {
console.log('There was an error fetching from database', error);
}
}
);
}
in render part, I wrote:
{this.state.subdata.map((rb,index)=>{
return <li><div>{rb.name}</label></div></li>})
}
Here comes the question, I still do not know how to create the tree recursively(because any node might has its children nodes ). how to do this when we can only get a node's children nodes from the database?
I would do your task in two steps:
Create a structure for an augmented tree with loading status flags. It should have a structure like this (this is pseudocode):
class Node {
loaded: boolean,
expanded: boolean,
children: list<Node>
}
Create a component for this:
If node isn't expanded don't render its children
If use clicks on expand sign
If children are loaded, do nothing, just change the expanded field
If children aren't loaded
set expanded to true
initiate ajax request
as soon as the request completes, set loaded to true, and assign children
Creating a component which recursively uses itself isn't a problem. If you don't know how to do this read here: how to render child components in react.js recursively
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.
The various inputs on my page are bound via knockout to a view model, let's say a customer record. That's all working fine.
Now, I want to put a SELECT at the top of the page that contains a list of all customers. The user will pick a customer, the record will be fetched from the database, and the data will be bound to the view model.
My question concerns conditional styling of the items in that SELECT list. It will be bound to an array of customer objects. The Customer object definition has a function called hasExpired:
var Customer = function (id, name, expiryDate) {
this.id = id;
this.customerName = name;
this.expiryDate = expiryDate;
this.hasExpired = function() {
return this.expiryDate == null ? false : true;
};
};
The ViewModel, to which the inputs on the page are bound, looks like this:
function ViewModel() {
var self=this;
self.customerRegion = ko.observable(),
self.customerName = ko.observable(),
.
.
.
self.allCustomers = Customers, // Customers is an array of Customer objects
self.selectedCustomer = ko.observable()
}
This knockout binding works; the SELECT is correctly populated with the list of customers:
<select id="customerSelect"
data-bind="options: allCustomers,
optionsText: 'customerName',
value: selectedCustomer />
I want to style the individual OPTIONS, adding an "expired" class if appropriate.
The individual items in the Customers SELECT are not bound to the view model. The SELECT functions like a navigation menu. The options are bound to the customer objects in the allCustomers array.
How to tell knockout to consult the hasExpired property of the customer object bound to each OPTION, to determine whether that particular option should get the expired property?
I want the customer to remain in the Select list but to appear with strike-through formatting.
Does the SELECT require its own view model?
The options binding has a parameter (optionsAfterRender) that allows for additional processing of the options elements. See Note 2: Post-processing the generated options (via the linked documentation).
Unless I have misinterpreted the structure of your data models, all that is required is a callback
self.setOptionStyling = function(option, item) {
ko.applyBindingsToNode(option, {css: {expired: item.hasExpired()} }, item);
}
bound to the optionsAfterRender parameter:
<select id="customerSelect"
data-bind="options: allCustomers,
optionsText: 'customerName',
value: selectedCustomer,
optionsAfterRender: setOptionStyling" />
Where the expired css class is defined as:
.expired {
text-decoration: line-through;
}
Fiddle