Develop Reference

Can't convert object of type java.lang.String to type com.thesis.joinerapp.Model.Joins

So i want to query my Firebase Database base on the value that i get from other activity.
private String tripID = "";
tripID = getActivity().getIntent().getStringExtra("tripID");
JoinRef = FirebaseDatabase.getInstance().getReference().child("Join").child(tripID);
FirebaseRecyclerOptions<Joins> options = new FirebaseRecyclerOptions.Builder<Joins>().setQuery(JoinRef,Joins.class).build();
Database Structure:
But it shows an exception
com.google.firebase.database.DatabaseException: Can't convert object
of type java.lang.String to type com.thesis.joinerapp.Model.Joins

While FirebaseUI can perform look ups of data for you, your data has to be in a very specific format for that.
If you want to show a subset of the number of trips, the index has to look like this:
"myTrips": {
"tripID1": true,
"tripID2": true
}
Where tripID1 and tripID2 are the -L keys that you have under /Trip.
You can find another example of this data in the FirebaseUI documentation on showing indexed data.

when you want to use the FirebaseUi, your database structure should be like this.
{
"Join" : {
"tripID" : {
"pushUid" : {
"joinID" : "yourJoinID",
"personCount" : "1",
"tripID" : "yourTrioID",
"uid" : "yourUid"
}
}
}
}
You need to add new root child which is pushId.

Firebase Realtime Database Filter Data in Nested List

I wanted to retrieve filtered data from db according to extra_Cat value like 31
I am able to retrieve full data easily but unable to put filter in it
Note: I have checked almost every solution, If duplicate please reply then tag duplicate
my code is
DBConnection dbConnection=new DBConnection();
postRef=dbConnection.database.getReference("Data");
postRef.child("extra_Cat").orderByKey().equalTo("*31*").limitToLast(500).addValueEventListener(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
long as= dataSnapshot.getChildrenCount();
Log.d("Data", String.valueOf(as));
}
#Override
public void onCancelled(DatabaseError error) {
// Failed to read value
}
});
and JSON is
"32161" : {
"author_name" : "Talented+Desk",
"cat_ID" : "%2A7%2A",
"cat_name" : "%E0%A4%96%E0%A5%87%E0%A4%B2",
"content" : "A4%B5A4%A8%E0%A4%BF%E0%A4%AF%E0%A4%AE+%E0%A4%B9%E0%A5%88%E0%A4%82%7C%E2%80%9D%3C%2Fp%3E%0A",
"extraCat" : [ "*31*", "*14*" ],
"fea_image" : "https%3A%2F%2Fwww.talentedindia.co.in%2Fwp-content%2Fuploads%2F2018%2F03%2Faajeevan-pratibandh-Steve-Smith.jpg",
"post_comment" : "0%A4%BF%E0%A4%AF%E0%A5%8B%E",
"post_date" : "2018-03-26",
"post_id" : "32161",
"post_slug_name" : "kangaroos-protest-against-less-punishment",
"post_status" : "publish",
"post_time" : "10%3A45%3A40",
"post_video" : "",
"slider_image1" : "",
"slider_image2" : "",
"slider_image3" : "",
"slider_image4" : "",
"title" : "%E0%A4%94%B8%E0%A4%9C%E0%A4%BE+%E0%A4%AA%E0%A4%B0+%E0%A4%B5%E0%A4%BF%E0%A4%B0%E0%A5%8B%E0%A4%A7"
},

You cannot create a query based on values that exist within an array. As I see in your database, extraCat is an array which contains 2 values, *31* and *14*.
In order to solve this, you need to change your database structure a little bit. So your extraCat node should look like this:
extraCat
|
--- "*31*": true
|
--- "*14*": true
As you can see, the extraCat node the is now a Map. The corresponding query should look like this:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
Query query = rootRef.child("Data")
.orderByChild("extra_Cat/*31*")
.equalsTo(true)
.limitToLast(500)
.addValueEventListener(/* ... */)

First you are using wrong reference path. The current you are using is Data/extra_cat. As I see in your Firebase structure it should be Data/32343/extraCat.
You can't use .child("extra_Cat").orderByKey().equalTo("*31*") because the *31* is not of the extra_Cat keys value. The value is in the list.

Getting rank of user from firebase database in android

I have a real time firebase database that stores a list of users and it's stored in the following format(Json)
{
"users" : {
"-L29HeOZCmYu9UGJLMQR" : {
"name" : "John Doe",
"phoneNumber" : "+555-1566",
"points" : 21,
"rank" : 10,
"userId" : "-L29HeOZCmYu9UGJLMQR"
},
"-L2ASCuStoH7CTaqgBgG" : {
"name" : "Jenna Rose",
"phoneNumber" : "+555-3562",
"points" : 96,
"rank" : 0,
"userId" : "-L2ASCuStoH7CTaqgBgG"
},
....// A lot more users.
}
So my question is, how do I get the rank of the user in terms of the "points" variable? Also, how do I prepare a list of the top 10 or the top 100 etc..?

There is no way to get the rank of a specific user, without loading all users.
But you can get the top N users by using Firebase's query mechanism to sort and filter data. For example:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("users");
Query top10query = ref.orderByChild("points").limitToLast(10);
top10query.addChildEventListener(...
The children will be in ascending order. You'll have to revert them client-side, for example by adding each subsequent child to the top of the list.

Firebase data sorting by date stamp

Ia am working on an app that receives datamessages with timestamp in the format "yyyy/MM/dd kk:mm:ss". here is the JSON data format.
"NOT20170828132901" :
{
"code" : "Your order status has been updated to Rejected",
"date" : "2017/08/28 13:29:01",
"title" : "Order update SPB20170825095233542"
}
i want to sort the NOTNUMBER based on the latest timestamp. I tried with limitToLast(i) and also limitToFirst(i) but in vein. The result is Ascending order. Iwant the datestamp to be sorted in Descending order. I also tried using startAt(futuredatestamp).endAt(pastdatestamp) but not working. I want to sort in this ay:
"NOT20170828140827" : {
"code" : "Your order status has been updated to Rejected",
"date" : "2017/08/28 14:08:27",
"title" : "Order update SPB20170825095233542"
},
"NOT20170828140436" : {
"code" : "Your order status has been updated to Delivered",
"date" : "2017/08/28 14:04:36",
"title" : "Order update SPB20170825095233542"
},
"NOT20170828132901" : {
"code" : "Your order status has been updated to Rejected",
"date" : "2017/08/28 13:29:01",
"title" : "Order update SPB20170825095233542"
},
"NOT20170828115852" : {
"code" : "Your order status has been updated to Rejected",
"date" : "2017/08/28 11:58:52",
"title" : "Order update SPB20170825095233542"
},
"NOT20170828014147" : {
"code" : "Your order status has been updated to IN TRANSIT",
"date" : "2017-08-28 01:41:47",
"title" : "Order update : SPB20170825095233542"
}
Little confused in using filter parameters.
Please help me. Thank in advance

Making an assumption that you are displaying the data from Firebase in a Recyclerview, add this code.
mLayoutManager = new LinearLayoutManager(MyActivity.this);
mLayoutManager.setReverseLayout(true);
mLayoutManager.setStackFromEnd(true);
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.setAdapter(yourAdapter);
What the code above does, it reverses the contents of the recyclerview.

The best practice to save date and time in a Firebase database, is to save it as a TIMESTAMP using ServerValue.TIMESTAMP like this:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
Map map = new HashMap();
map.put("time", ServerValue.TIMESTAMP);
yourRef.child("yourNode").updateChildren(map);
Remember, you are saving the TIMESTAMP as a Map but you are retrieving it as a long. To get the data back, i suggest you using this method:
public static String getTimeDate(long timeStamp){
try{
DateFormat dateFormat = getDateTimeInstance();
Date netDate = (new Date(timeStamp));
return dateFormat.format(netDate);
} catch(Exception e) {
return "date";
}
}
Then the orderBy() method in your query will work for sure.

How to paginate in Firebase Database #AskFirebase

I am creating an application that is some kind of a personal vocabulary. The database is of the following form.
Now I need to implement a pagination, partial retrieval of the words of a user, but preserving the lexicographical order. Keeping words as keys (/user/{uid}/words/{word}) is not suitable, because handling homographs will be impossible in the future (as their key will coincide). I decided to keep additional property word for each user, so that I can call db.getReference().child("users").child(uid).child("words").orderByChild("word").
This will retrieve all words of a user. Now I need to paginate this query, e.g. first download 20 words and then again 20 etc., but preserving lexicographical order.
{
"users" : {
"yXYSqB016JMr1FIc85pvMbvqDDt2" : {
"words" : {
"5v1a1PaDKnTvvOH19kaFTa1iyOx2" : {
"index" : 1,
"word" : "apple"
},
"kXHakBKxk9TrAlWL1vTOCe0akk80" : {
"index" : 2,
"word" : "house"
},
"xSKSqB312JMrsFig15pvMbvqAAt0" : { ... }
}
},
"zCAtMpl9uxSjG9dJarGktTTs20w2" : { ... }
},
"vocabulary" : {
"en" : {
"5v1a1PaDKnTvvOH19kaFTa1iyOx2" : {
"definitions" : {
"a fruit that grows on a tree" : true
},
"word" : "apple"
},
"kXHakBKxk9TrAlWL1vTOCe0akk80" : { ... },
"xSKSqB312JMrsFig15pvMbvqAAt0" : { ... }
}
}
}

You seem to come from a SQL way of thinking, where you paginate by specifying the number of items to get and the number of items to skip. This is index-based pagination.
Firebase on the other uses cursor-based pagination. You tell it the nimber of items to get and at which item to start (or end). You identify this item by the value of the property on which you order, in your case that is the value of word. Since the same value could potentially appear in multiple children, you can also specify the key (the thing starting with 5v1a1...) of the child at which to start/end as a second parameter.
So say that you have a page size of two. You get the first 2 words with:
DatabaseReference allWords = db.getReference().child("users").child(uid).child("words");
Query firstPage = allWords.orderByChild("word").limitToFirst(2);
When you attach a listener to this, you'll get the first two words. You'll need to remember the word and the key of the last word in this first page:
String lastWordOnPreviousPage = "house";
String lastKeyOnPreviousPage = "5v1a1...";
Now if you need the second page of two words, you get them by:
Query secondPage = allWords.orderByChild("word").startAt(lastWordOnPreviousPage, lastKeyOnPreviousPage).limitToFirst(2);