Advertissement: I'm using CouchbaseLite Android 1.4.0 and I'm not ready to switch to 2.0.
To get the context of my issue:
I have 2 doc types: PATIENT & VISIT
A patient is linked to a visit by a field visitId
A visit has a startDateTime and a endDateTime
A visit is considered as 'open' if the endDateTime is null or missing
A visit can be of different types through the field visitType
A visit can be inactive through the field inactive
I want to:
Get all patients (id + name) of all open and active visits of a certain type
The result is paginated using skip and limit
Get the result sorted by name
I managed to get all the correct patients and to paginate the result but the issue is with the sorting.
I can't make a 'post sorting' (getting the result in a random order and then use self-made method to sort them) because of the pagination.
So here is how it works actually without the sorting:
THE MAP/REDUCE
if (isVisit()) {
Object inactive = document.get(FIELDS.INACTIVE);
if(inactive == null)
inactive = false;
Document patientDoc = database.getExistingDocument(FIELDS.PATIENT_ID);
if(patientDoc != null && patientDoc.getProperties() != null) {
Object[] keys = {
document.get(CouchbaseVisitManager.FIELDS.STOP_DATE_TIME),
inactive,
document.get(CouchbaseVisitManager.FIELDS.VISIT_TYPE)
};
Object[] values = {
document.get(FIELDS.PATIENT_ID),
patientDoc.getProperties().get(FIELDS.FAMILY_NAME),
patientDoc.getProperties().get(FIELDS.FIRST_NAME)
}
emitter.emit(keys, values);
}
}
THE QUERY
Query query = getQuery(Views.PATIENTS_CURRENTLY_IN_VISIT); //Helper method to create a query
query.setKeys(new ArrayList<Object>(){{
add(new ArrayList<Object>(){{
add(null);
add(false);
add(visitType);
}});
}});
query.setSkip(skip);
query.setLimit(limit);
And this is working well to get my patients but not for sorting them.
I tried to add patient names inside the view like this:
Object[] keys = {
patientDoc.getProperties().get(FIELDS.FAMILY_NAME),
patientDoc.getProperties().get(FIELDS.FIRST_NAME),
document.get(FIELDS.STOP_DATE_TIME),
inactive,
document.get(FIELDS.VISIT_TYPE)
};
And update my query.keys like this:
query.setStartKey(new ArrayList<Object>(){{
add(null);
add(null);
add(null);
add(false);
add(visitType);
}});
query.setEndKey(new ArrayList<Object>(){{
add(new HashMap<>());
add(new HashMap<>());
add(null);
add(false);
add(visitType);
}});
But this returns no patients (result.size = 0)
So... I don't know how to achieve my goal.
I tought of a way to sort by values but it doesn't seem to exist yet (should wait for 2.0 I think). But is their any workaround to achieve this kind of behavior?
Thank's for reading.
View results are always sorted by key. So you should add the patient name to the key and then you'll get your sorting.
Be careful to put the name into the correct place of the keys array since the sorting is lexicographical, that is if the name is going to be the last component then you'll get all open inactive sorted by name, then all open active sorted by name e.t.c.
In case you need to put your name key in front of the other keys but still be able to filter your results, then you will need to properly construct the start key and the end key so that the full range of every possible patient names would be accepted while the later keys would be filtered.
You will have to provide some values which will definitely be less than or greater than any possible patient name.
Following the key collation defined for Couchbase views, a null will be always less than any string, and an empty map {} can be used to match past the last string. You are basically doing it right in your last sample.
Don't forget to switch the start and end keys logic if you would like to query the view in reverse mode
Another thing to take care of is always incrementing the version of the view after changing its logic or key set, otherwise you will continue getting old results. Incrementing the version will force a refresh of the view, executing the updated logic in the view function over all your data.
I am a bit new to Firebase and so have been playing around with to help myself get more acquainted with it. So while I was playing around with realtime databases, I was trying to append data to the JSON tree. The code is as below
mSaudi.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
count++;
mHistory = mChildRef.child(Integer.toString(count));
current = riyadh;
mChildRef.setValue(riyadh);
mHistory.push().setValue("riyadh");
}
});
The tree which I require is something like this:
value:
1: some text
2: some other text
But what's a actually happening is this:
value:
1: some text
and on updation
value:
2:some text
the previous entry gets erased
I have tried changing the references in various ways but to no avail. Any help in this regard would be appreciated.
If you would like to save both values, you have to save them using a variable such as a Hashmap. If you save a string and then try save another one under the same branch, it will delete everything previously saved. So try the following
HashMap<String, String> map = new HashMap<>();
map.put("1","String");
map.put("2","String");
mHistory.push().setValue(map);
This will save both the strings without deleting one.
If you would only like to add one String
mHistory.push().child("1").setValue("Your first String");
The biggest problem with this though is that everytime you use push() you generate a random key, so you would have to save the key as a string and use it as a reference in your child.
When you set a value on Firebase, it is going to replace everything in, and under the reference.
Let's say that you have a house value, with 2 childs: Color and Size.
If you want to edit only the color value, before the setValue(), you will have to change the reference you are pushing to.
If your reference was getReference().child("houses") and you push something there, it's going to replace everything there and below it. The way to do it is create a new reference (or update the previews one) like this: getReference().child("houses").child(houseKey).child("color") and push your String there.
In your example, you will need to add the field you want to change as a child before the push() method.
The other way was already told by #Janwilx72 and is getting the whole object, updating the value locally and pushing the entire object again.
You can try this
mChildRef.child("2").setValue("some text");
It should be appending new item instead of overwriting them
I have (somewhat) large list of jokes in my Firebase Database like in the image below.
I display them in a list in my Android app something like a feed. I also implemented possibility to log in with Firebase Authentication and now I want to add options for logged users to (dis)like jokes and add them to favorites (favorites are supposed to be like private bookmarks). I'm wandering how I could structure my data and I have two proposals:
Add new root node called "userJokes" with child nodes representing user UID from Firebase Authentication. Every UID child node should have copy of every joke from "joke" node with additional booleans representing (dis)like and favorite states.
Another solution is to add every user UID to a joke a user (dis)likes or adds to favorite.
First solution is logical, but how could I count number of likes and dislikes if I structure data this way? And what is the best way to copy every joke from "joke" node to "userJokes" node for every user to be showed in the feed? Second is impractical since while retrieving jokes, I will get info about every user that has (dis)liked or added to favorites and this is not what I need. Which solution is better? Is there any other? Is it OK to add user UID from Firebase Authentication to database in Firebase Database?
I think the first one is more accepted, although it needs some tweak :)
First note: if you create data only to be used as relational (like userJokes), it's better to just add simple value to it without copying entire source data (jokes data), like this:
userJokes: {
randomUserId: {
randomJokeId:true,
anotherRandomJokeId:true
}
awesomeUser: {
randomJokeId:true
}
}
Second note: if you want to implement two functionality (like and favorite), I think you should make it as different data. So it would be userJokeLike and userJokeFavorite (or something like that). And the structure for each of them should be same as I mentioned in first note.
In conclusion:
Every joke data is still in their source path (i.e. inside jokes) and ONLY their id is copied into newly created data path (userJokeLike and userJokeFavorite)
When you want to search for joke that user with id randomUserId likes, you should check for userJokeLike\randomUserId. Then from every joke id you got there, get the real data from inside source jokes path.
When you want to search for joke that is favorited by user with id randomUserId, basically, do the same as above.
When you want to count likes and favorite of each joke, just use something like this:
FirebaseDatabase.getInstance().getReference("userJokeLike")
.orderByChild().equalsTo("randomJokeId")
.addListenerForSingleValueEvent(new ValueEventListener() {
... onDataChange(DataSnapshot dataSnapshot) {
int jokeCount = dataSnapshot.getChildrenCount();
}
});
And there you go, hope this helps.
Note: I haven't check the last code, hope that work :p
EDIT:
Looks like I did misunderstand :D
The solution above is what I think is best for the sake of structure itself. But if we need something simple and fast, it is different for each case/situation. I think that the best solution if you want to get jokes with likes and favorites included (no need to create another request) then your structure should look like this:
jokes: {
randomJokeId: {
// joke data here
likes:{
randomUserId:true,
anotherUserId:true
},
favorites:{
randomUserId:true
}
}
}
It includes likes and favorite when you request jokes data. SO in each data you only need to check if current user's UID is exist inside likes and/or favorite. And the counter will be a lot easier this way.
Happy coding :)
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.
I have a simple firebase database: /rides is a list of simple objects like this
{
car: "Toyota"
minutes: 15
}
and I need to display sum of minutes of all the rides. The obvious solution is to load all the rides and calculate the sum. But if I have several hundreds of rides this is very slow, up to several seconds.
So it seems I have to maintain a separate field /totalMinutesin the database for this. But thus I will have to manually update /totalMinutes every time I add/remove/change a ride. Anyway this is not a big deal of work.
But what if I need to calculate total minutes only for a subset of rides? For instance only for "Toyota" cars or "Ford" cars? Manual maintaining /totalMinutesFord, /totalMinutesToyota now doesn't seem so easy.
So what is the correct way to maintain such dynamic values in firebase?
Firebase has no way to get automatically calculate values based on the data in your database.
So your two options are:
calculate the value whenever you update the data
retrieve all the data and calculate the value on the client
You already (wisely) decided that retrieving all data is not a good idea. Your users will be grateful for that.
So that leaves calculating the derived values whenever you update the data of a ride. I'm not sure why doing that for multiple values would be more difficult than doing it for a single value. It may be more code, but it's pretty much the same code:
var ride = { car: "Toyota", minutes: 15 };
ref = new Firebase('https://yours.firebaseio.com/');
ref.child('rides').push(ride);
ref.child('totalMinutes').transaction(function(current_value) {
return (current_value || 0) + ride.minutes;
});
ref.child('totalMinutes'+ride.car).transaction(function(current_value) {
return (current_value || 0) + ride.minutes;
})