Develop Reference

Is there any query to retrieve the data present in list firebase android

I want to retrieve only that post where postCategory matches the user interest.
How can I achieve this type of query. Any Help??
Below is my json file of database..
"Posts" : {
"-MAKobGjdhMfJFwZ1kol" : {
"postCategory" : "Animals",
"postDesc" : "still",
"postImage" : "Image Link",
"postPersonName" : "Name",
"postPersonUid" : "CLQA22uZpLS1ErIrnoBTrC3xqBw2",
"postTitle" : "ek"
},
"Users" : {
"CLQA22uZpLS1ErIrnoBTrC3xqBw2" : {
"email" : "email",
"interest" : {
"-MA14zFcNfs1JAjux129" : {
"name" : "Developer"
},
"-MA14zFgzhL-MOBB7D6h" : {
"name" : "Shopping"
}
},
"name" : "Name",
"uid" : "CLQA22uZpLS1ErIrnoBTrC3xqBw2"
}

In firebase database you cannot have such queries.
You should use Firestore (https://firebase.google.com/docs/firestore) for such advanced queries.
firestore/query-data
firestore

To get all posts with postCategory equal to Animals, you'd do:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference("Posts");
Query query = ref.orderBy("postCategory").equalTo("Animals");
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for (DataSnapshot postSnapshot: dataSnapshot.getChildren()) {
Log.i(TAG, postSnapshot.getKey()+": "+postSnapshot.child("postTitle").getValue(String.class));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
}
If you want to retrieve posts for multiple categories, you'll have to perform a separate query for each of those and merge the results on your client.
I'd also recommend changing how you store the categories for a user. The idiomatic way is:
"Users" : {
"CLQA22uZpLS1ErIrnoBTrC3xqBw2" : {
"email" : "email",
"interest" : {
"Developer": true,
"Shopping": true
}
},
The reasons this is more common is that it automatically ensures that each value can occur only once in the interest object, since property names are by definition unique.

It is possible to retrieve in such a way data from Firebase?

I would like to know how can I retrieve the key of this object based on the object content. I'm using a realtime firebase database.
JSON code :
"Places" : {
"-M11-OIIHbKTVqCJ-Swv" : {
"name" : "Farmacia Pagani Dr. Roberto",
"others" : {
"Abilify" : 100,
"Acetaminophen" : 120,
"Acyclovir" : 140,
"Adderall" : 160
}
},
"-M11-OJJCGAPdJUknLXX" : {
"name" : "FARMACIA DR. TUMIATTI MARIANO",
"others" : {
"Abilify" : 100,
"Acetaminophen" : 120,
"Acyclovir" : 140,
"Adderall" : 160
}
}
I want to retrieve M11-OIIHbKTVqCJ-Swv if I have the name : Farmacia Pagani Dr. Roberto"
The code I wrote :
mUserDatabase = FirebaseDatabase.getInstance().getReference("Places");
Query query = mUserDatabase.orderByChild("name").equalTo(nameOfThePharmacy);
query.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println("The key is : "+dataSnapshot.getKey());
}
#Override
public void onCancelled(DatabaseError databaseError) {
throw databaseError.toException();
}
});
This code doesn't work, it returns : "Places" but I want the key of the object that contains the field name that equals with = ad example Farmacia Pagani Dr. Roberto , the output should be : -M11-OIIHbKTVqCJ-Swv

What is construction of Json DB for Android Firebase Realtime Database?

I uploaded such json to firebase console of realtime database. And to get some "words" im trying get child "words" with orderByChild ... startAt and so on...
Someone on this forum told me there is no any child in "words". Whats wrong?
{
"words" : {
"1" : {
"id" : 1,
"lang1" : "s1",
"lang2" : "d1",
"type" : "a"
} ,
"2" : {
"id" : 2,
"lang1" : "s2",
"lang2" : "d2",
"type" : "a"
} // ...
}
}
And my Java code:
Query fb = FirebaseDatabase
.getInstance()
.getReference()
.child("words")
.orderByChild("lang1")
.startAt("s2")
.limitToFirst(20);
BTW. I can not get any responce. This listener does not return anything.
fb.add... ValueEventListener() {
... void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
Word w = singleSnapshot.getValue(Word.class);
Log.i(TAG, new Gson().toJson(w));
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
Log.w(TAG, "onCancelled", databaseError.toException());
}
});

Android - Save list of object property with specific key on Firebase

Let's consider a "UserBean" with a property "emails" that is an ArrayList<EmailBean>.
When saved in Firebase it's like :
"users" : {
"$userID" : {
"emails" : [
"0" : {
"type" : "first",
"address" : "google#google.com",
"private" : true
},
"1" : {
"type" : "second",
"address" : "firebase#firebase.com",
"private" : false"
}
],
"name" : "Mitch"
}
}
So is it possible to achieve something like this :
"users" : {
"$userID" : {
"emails" : [
"first" : {
"address" : "google#google.com",
"private" : true
},
"second" : {
"address" : "firebase#firebase.com",
"private" : false
}
],
"name" : "Mitch"
}
}
I would prefer to not having to save each address one at a time.
Maybe there's an annotation to tells Firebase to use this property as a key ?
Regards.

I recomend you using the code below:
DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference emailsRef = rootRef.child("users").child(userId).child("emails");
ValueEventListener eventListener = new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot ds : dataSnapshot.getChildren()) {
String type = ds.child("type").getValue(String.class);
ds.child("type").getRef().getParent().setValue(type);
}
}
#Override
public void onCancelled(DatabaseError databaseError) {}
};
emailsRef.addListenerForSingleValueEvent(eventListener);
What have i tried with this code? So in order to achieve what you want, first of all we got the value of your type key. Then we get a step up in the tree and set the partent with the value of your type key for each particular node.
Having the value of type in stead of 0, 1 and so on, to get the work done, just remove the type key, from each node using removeValue() method directly on the reference.

Query to retrieve specific data from Firebase

I am creating an android app and I am stuck at a problem. In order to explain the problem, I would like to show my database structure
{
"EXlzg1COUbOhQjwPCGbS1NRdp5H3" : {
"Contacts" : {
"Contact1" : value (Contact number)
"Contact2" : value
"Contact3" : value
},
"name" : "Sagar Khan",
"phone" : 7276273667
},
"OLm7VWsMcGQpterECyhJ8YTSPna2" : {
"Contacts" : {
"Contact1" : value
"Contact2" : value
"Contact3" : value
},
"name" : "Sameer",
"phone" : 8412914728
},
"TXanCkqtB5PdEogtv8Dzw8y1ngw1" : {
""Contacts" : {
"Contact1" : value
"Contact2" : value
"Contact3" : value
},
"name" : "Harish",
"phone" : 7020743544
},
"qnDVoc72nXa8XvOH1L39VvqFzKL2" : {
"Contacts" : {
"Contact1" : value
"Contact2" : value
"Contact3" : value
},
"name" : "Harish Shinde"
"phone": 8149870822
}
}
This is very short structure the actual one is to big
Now what I want to do is I want to fetch only those users whose contact number is present in current user node and display those users in a Android list.
For example:
User 1 with id EXlzg1COUbOhQjwPCGbS1NRdp5H3 is having 3 contacts
"EXlzg1COUbOhQjwPCGbS1NRdp5H3" : {
"Contacts" : {
"Sameer" : 8412914728 (Contact number)
"Contact2" : value
"Contact3" : value
},
"name" : "Sagar Khan",
"phone" : 7276273667
},
Now when I will fetch the list of users from my database and show it in my Android app list, I want only those users to be added whose contact number is present in User 1 contacts.
My problem is that I literally don't know how to do this as I am new to Android development and Firebase. I am clear with the read and write basics of Firebase, but such operations, I have no idea how to do it.
I have searched a lot, but cannot find any solutions or examples. A detailed description will be very good for me. ;) Thanks in advance.

Here's the change I propose:
This is the new database structure for Users node:
"Users" : {
"EXlzg1COUbOhQjwPCGbS1NRdp5H3" : {
"name" : "Sagar Khan",
"phone" : 7276273667
},
..
}
And the contacts of the user "Sagar Khan" will be stored in another node called Contacts under that user's UserID (EXlzg1COUbOhQjwPCGbS1NRdp5H3) :
"Contacts" : {
"EXlzg1COUbOhQjwPCGbS1NRdp5H3" : {
"Contact1":{
"name" : "Sameer",
"phone" : 7276273000
},
"Contact2":{
"name" : "Alice",
"phone" : 7276273600
},
...
},
//other user id with their contacts
...
}
I suspect that the user ID (eg: EXlzg1COUbOhQjwPCGbS1NRdp5H3) is taken from a logged in user, using:
mAuth.getCurrentUser().getUid();
Therefore, to get the contacts of a logged in user you can query the database like this:
DatabaseReference mUserContactsRef = FirebaseDatabase.getInstance().getReference().child("Contacts").child(mAuth.getCurrentUser().getUid(););
mUserContactsRef.addListenerForSingleValueEvent(new ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
for(DataSnapshot userContact : dataSnapshot.getChildren()){
Contact contact = userContact.getValue(Contact.class);
//add each contact to an arraylist and use it to populate a list of contacts
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
You can add each contact object to an ArrayList and use it to populate a list. The key is the User ID, you can access anything related to a user using the UserID.
This is the approach I recommend and what I have used in the past successfully for similar scenarios.