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 attempting to access the attributes of the first datum only in a Firebase snapshot which consists of 10 URLs. No matter what I try, however, I am getting the whole snapshot. My code looks like:
myDataRef.limitToLast(10).on("child_added", function(snapshot) {
var newImg = snapshot.child("url");
console.log(newImg);
});
Is there a way to specify [0] or the like on the whole snapshot so that I'll just get the first datum?
It's tricky to be sure without seeing your data structure, but I think you're looking for:
myDataRef.limitToLast(10).on("child_added", function(snapshot) {
var newImg;
snapshot.forEach(function(urlSnapshot) {
if (!newImg) {
newImg = urlSnapshot.val();
}
});
console.log(newImg);
});
The forEach() loops over all child keys of the snapshot and invokes the inner callback with a DataSnapshot of each of them.
The newImg = urlSnapshot.val(); will just get the value of that child. You may have to modify this bit based on your data structure.
Let me preference this by saying there is no guaranteed order for how data is stored in firebase - the concept of first item or index 0th item is determined by how the data is stored and how the data is retrieved.
So the best bet is to either load all the values as a snapshot and sort by a specified value (like date or height etc) and pick off the 0th index from the sorted array, or load in a subset of data and use queryOrderedByChild or queryStartingAtValue
This may be an answer to the question: it does retrieve only the first value within a specified node:
users
user_0
firstName: "Fred"
user_1
firstName: "Bill"
user_2
firstName: "Ted"
and the code
usersRef.observeSingleEventOfType(.ChildAdded, withBlock: { snapshot in
if snapshot.value is NSNull {
print("snapshot was NULL")
} else {
print(snapshot)
}
})
and the result
Snap (user_0) {
firstName = Fred;
}
You would need to store the snapshot as an array first and access it as [0].
I'm not at my mac computer (I'm answering your question as for iOS, but I believe the concept is the same) so this is just from my memory, but it works if the syntax is correct:
var newImgArray = snapshot.children.objects as? [FSSnapshot]
var newImg = newImgArray[0].value
I was checking the firebase docs looking for how to get the number of items saved in my DB according to a query and I looked at this piece of code that has (I think) exactly what I'm looking for, but dont know how to get the numbers of items displayed.
var ref = new Firebase("https://dinosaur-facts.firebaseio.com/dinosaurs");
ref.orderByChild("height").equalTo(0.6).on("child_added", function(snapshot) {
console.log(snapshot.key());
});
The console.log should display 2 items as there are 2 dinosaur with that height. So how can I get the number of items displayed to show it on the view?
I tried with console.log(snapshot.key().length); but it displays a wrong number
When you listen for the child_added event, the number of items in your callback will always be 1. This is great for when you (for example) want to add each item to a list. But it's not great when you want to count the number of items.
For operations that need to handle multiple items, it's easier to listen to the value event:
var ref = new Firebase("https://dinosaur-facts.firebaseio.com/dinosaurs");
ref.orderByChild("height").equalTo(0.6).on("value", function(snapshot) {
console.log(snapshot.numChildren());
})
This snippet also shows the other piece of the puzzle: DataSnapshot.numChildren().
You can try this:
var ref = new Firebase("https://dinosaur-facts.firebaseio.com/dinosaurs");
var shortDinosaurs = ref.orderByChild("height").equalTo(0.6);
console.log(shortDinosaurs.length);
shortDinosaurs.on("child_added", function(snapshot) {
console.log(snapshot.key());
});
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.
Am working on a windows store javascript application. The application uses data from azure mobile services.
Consider the below code:
var itemTable = mobileService.getTable('item');
//item is the table name stored in the azure database
The code fetches the entire table item and saves it to a variable itemTable.
What code will return the no of rows present in itemTable??
What you're looking for is the includeTotalCount method on the table/query object (unfortunately it's missing from the documentation, I'll file a bug to the product team to have it fixed).
When you call read on the query object, it will return by default 50 (IIRC, the number may be different) elements from it, to prevent a naïve call from returning all elements in a very large table (thus either incurring the outbound bandwidth cost for reserved services, or hitting the quota for free ones). So getting all the elements in the table, and getting the length of the results may not be accurate.
If all you want is the number of elements in the table, you can use the code below: returning zero elements, and the total count.
var table = client.getTable('tableName');
table.take(0).includeTotalCount().read().then(function (results) {
var count = results.totalCount;
new Windows.UI.Popups.MessageDialog('Total count: ' + count).showAsync();
});
If you want to query some elements, and also include the total count (i.e., for paging), just add the appropriate take() and skip() calls, and also the includeTotalCount as well.
If anybody comes here and interested in how to get the totalCount only on C# (like me), then this is how you do it:
var table = MobileService.GetTable<T> ();
var query = table.Take(0).IncludeTotalCount();
IList<T> results = await query.ToListAsync ();
long count = ((ITotalCountProvider)results).TotalCount;
Credit goes to this blog post here
You need to execute read() on the table query and then get the length of the results.
var items, numItems;
itemTable.read().then(function(results) { items = results; numItems = items.length; });
If you are only showing a record count and not the entire results - you should just select the ID column to reduce the amount of data transmitted. I don't see a count() method available yet in the JS Query API to fill this need.
var itemTable = mobileService.getTable('item').select('itemID');