I'm trying to learn how to connect my android application to the firebase database. I've tried the following code:
mDatabase = FirebaseDatabase.getInstance().getReference();
productCloudEndPoint = mDatabase.child("Sample");
productCloudEndPoint.push().setValue("Hello World");
However, nothing gets written when I look at the Firebase console. I have also set the rules.
{
"rules": {
".read": true,
".write": true
}
}
Am I missing something? Thanks
I had the same issue and the problem was that I was using the simulator. You have to use a physical device.
Do not use push method when you are using set() method, set() method would set the value to the reference.
ex:
<database-ref>/users/{UserId}/
username: {name}
Query would be:
mDatabase.child("users").child(userId).child("username").setValue(name);
In your case :
mDB.child("sample").setValue("Hello World");
While push method used to post new custom object, Firebase generates unique id and save into list of such objects.
NOTE: Push() method is used fro javaScript.
Example :
You have user object with properties like
Class User{
String name;
String email;
}
To save such object, you can simply use push() method.
Firebase will save it with a unique Id auto generated.
<db-ref>/users/{uniqueId}/
For JAVA: equivalent method is put() method.
Related
I dont know what is this thing is called but i want to get a refrence of it in android so i want to know what exactly is this thing is called , please check the image down
im taking about this line above "Quote" , whaat is this line is called and how do i get a databse refrence of it in android and really sorry for that bad handwriting though
right now i want to get refrence of 'Quote" im doing it like this
databaseReference = FirebaseDatabase.getInstance().getReference("Quotes");
but how can i get a refrence of that line above"Quote"
databaseReference = FirebaseDatabase.getInstance().getReference("What should i put here to get that refrence ?");
Seems you are using realtime database that is called firebase reference url
you can try as:
import { getDatabase, ref, child, get } from "firebase/database";
const dbRef = ref(getDatabase());
get(child(dbRef, `users/${userId}`)).then((snapshot) => {
if (snapshot.exists()) {
console.log(snapshot.val());
} else {
console.log("No data available");
}
}).catch((error) => {
console.error(error);
});
You can find your Realtime Database URL in the Realtime Database section of the Firebase console.
Depending on the location of the database, the database URL will be in one of the following forms: https:// DATABASE_NAME . firebaseio.com (for databases in us-central1 ) for more details on it you can access the documentation on
https://firebase.google.com/docs/database/web/read-and-write
If you want to get a reference to the root of the database, you can call getReference without any value:
rootReference = FirebaseDatabase.getInstance().getReference();
Also see the documentation for getReference() without parameters, which says:
public DatabaseReference getReference ()
Gets a DatabaseReference for the database root node.
Returns: A DatabaseReference pointing to the root node.
Currently, the Google's version of ServerValue.TIMESTAMP returns {".sv":"timestamp"} which is used as a directive for Firebase to fill that field with the server timestamp once you save the data to the Firebase server.
When you create your data on the client side however, you don't have the actual timestamp to play with yet (ie. use as the creation date). You only will have an access to the timestamp after the initial save and consequent retrieval, which - I imagine - is sometimes too late and not very elegant.
Before Google:
Update: Ignore this section as it is incorrect - I misunderstood the examples. ServerValue.TIMESTAMP always returned the {".sv":"timestamp"}.
As far as I understand in pre-google Firebase there seemed to be a server-generated timestamp available that allowed you to acquire the actual timestamp:
import com.firebase.client.ServerValue;
ServerValue.TIMESTAMP // eg. 1466094046
(ref 1, ref 2)
Questions:
Is such save/retrieval the only way to get the server-generated creation date on my model instances?
If yes can you propose a method of implementing such pattern?
Am I understanding correctly ServerValue.TIMESTAMP has changed with Google's acquisition of Firebase? Update: No, #FrankvanPuffelen replied that nothing's changed during acquisition.
Note:
I'm not considering using new Date() on client side as I've been reading it's not safe, though please share your thoughts if you think different.
When you use the ServerValue.TIMESTAMP constant in a write operation, you're saying that the Firebase Database server should determine the correct timestamp when it executes the write operation.
Let's say we run this code:
ref.addValueEventListener(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println(dataSnapshot.getValue());
}
public void onCancelled(DatabaseError databaseError) { }
});
ref.setValue(ServerValue.TIMESTAMP);
This will execute as follows:
you attach a listener
you write a value with ServerValue.TIMESTAMP
the Firebase client immediate fires a value event with an approximation of the timestamp it will write on the server
your code prints that value
the write operation gets sent to the Firebase servers
the Firebase servers determine the actual timestamp and write the value to the database (assuming no security rules fail)
the Firebase server send the actual timestamp back to the client
the Firebase client raises a value event for the actual value
your code prints that value
If you're using ChildEventListener instead of a ValueEventListener, then the client will call onChildAdded in step 3 and onChildChanged in step 8.
Nothing changed in the way we generate the ServerValue.TIMESTAMP since Firebase joined Google. Code that worked before, will continue to work. That also means that the first answer you linked is a valid way to handle it.
I'm doing it a bit differently.
Solution 1: push() method in POJO
As I don't want to clutter my POJOs with strange getters or properties, I'm just defining a push() method inside my POJOs which looks like this:
/**
* Pushes a new instance to the DB.
*
* #param parentNode `DatabaseReference` to the parent node this object shall be attached to
*/
fun push(parentNode: DatabaseReference) {
parentNode
.push()
.apply {
setValue(this#Pojo)
child(Pojo.CREATED_AT_KEY).setValue(ServerValue.TIMESTAMP)
}
}
Then I can simply create an instance of the POJO and call push() on it which properly populates the creation time property.
This definitely makes the POJO a little less plain and involves logic a POJO shouldn't know about. However using #Exclude annotations and/or casts as outlined in some of the responses here also requires knowledge of the storing mechanism.
Solution 2: Helper or DatabaseReference extension (Kotlin)
To overcome this you can of course also just create a pushTask(task: Task) method in a helper or - if using Kotlin - an extension method to e.g. DatabaseReference which could look like this:
fun DatabaseReference.push(pojo: Pojo) {
push()
.apply {
setValue(pojo)
child(Pojo.CREATED_AT_KEY).setValue(ServerValue.TIMESTAMP)
}
}
Looking at it now I come to think that I actually like the second approach more (if I have Kotlin at my disposal - I don't like helpers). But this is probably just a matter of taste. ;)
I read the firebase documentation: https://firebase.google.com/docs/database/android/retrieve-data
And I am still confused, on how to properly query just 1 object from my Firebase database.
Here is the lines of code I have written.
private Firebase mRef;
And in on start:
#Override
protected void onStart()
{
super.onStart();
//Firebase
mRef = new Firebase("my database url");
}
Then in onCreate or in onStart() I use this line:
Query myQuery= mRef.child("key to my DataObject");
But I get an error in that line, and the solution it provides me is:
change or migrate myQuery to com.firebase.client.Firebase
I am wondering which Query am I suppose to import? I have currently imported:
import com.google.firebase.database.Query;
Also, when I query an object, does something in my database have to change in order for me to retrieve objects?
Hopefully someone can provide clear and explicit example code Or steps to show how you query an object (im assuming you can just write a for loop to get a list of objects back).
Thanks
Assume your Firebase database has below structure:
{
"users" : {...}
}
then, to get reference of users, you should code as:
DatabaseReference mDatabaseReferenceUsers; = FirebaseDatabase.getInstance().getReference("users");
Now, If your users object contains a list, then you need to use push() method to get unique key and then set value as below:
String key = mDatabaseReferenceUsers.push().getKey();
mDatabaseReferenceUsers.child(key).setValue(new User("Bob", 27));
Currently, the Google's version of ServerValue.TIMESTAMP returns {".sv":"timestamp"} which is used as a directive for Firebase to fill that field with the server timestamp once you save the data to the Firebase server.
When you create your data on the client side however, you don't have the actual timestamp to play with yet (ie. use as the creation date). You only will have an access to the timestamp after the initial save and consequent retrieval, which - I imagine - is sometimes too late and not very elegant.
Before Google:
Update: Ignore this section as it is incorrect - I misunderstood the examples. ServerValue.TIMESTAMP always returned the {".sv":"timestamp"}.
As far as I understand in pre-google Firebase there seemed to be a server-generated timestamp available that allowed you to acquire the actual timestamp:
import com.firebase.client.ServerValue;
ServerValue.TIMESTAMP // eg. 1466094046
(ref 1, ref 2)
Questions:
Is such save/retrieval the only way to get the server-generated creation date on my model instances?
If yes can you propose a method of implementing such pattern?
Am I understanding correctly ServerValue.TIMESTAMP has changed with Google's acquisition of Firebase? Update: No, #FrankvanPuffelen replied that nothing's changed during acquisition.
Note:
I'm not considering using new Date() on client side as I've been reading it's not safe, though please share your thoughts if you think different.
When you use the ServerValue.TIMESTAMP constant in a write operation, you're saying that the Firebase Database server should determine the correct timestamp when it executes the write operation.
Let's say we run this code:
ref.addValueEventListener(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println(dataSnapshot.getValue());
}
public void onCancelled(DatabaseError databaseError) { }
});
ref.setValue(ServerValue.TIMESTAMP);
This will execute as follows:
you attach a listener
you write a value with ServerValue.TIMESTAMP
the Firebase client immediate fires a value event with an approximation of the timestamp it will write on the server
your code prints that value
the write operation gets sent to the Firebase servers
the Firebase servers determine the actual timestamp and write the value to the database (assuming no security rules fail)
the Firebase server send the actual timestamp back to the client
the Firebase client raises a value event for the actual value
your code prints that value
If you're using ChildEventListener instead of a ValueEventListener, then the client will call onChildAdded in step 3 and onChildChanged in step 8.
Nothing changed in the way we generate the ServerValue.TIMESTAMP since Firebase joined Google. Code that worked before, will continue to work. That also means that the first answer you linked is a valid way to handle it.
I'm doing it a bit differently.
Solution 1: push() method in POJO
As I don't want to clutter my POJOs with strange getters or properties, I'm just defining a push() method inside my POJOs which looks like this:
/**
* Pushes a new instance to the DB.
*
* #param parentNode `DatabaseReference` to the parent node this object shall be attached to
*/
fun push(parentNode: DatabaseReference) {
parentNode
.push()
.apply {
setValue(this#Pojo)
child(Pojo.CREATED_AT_KEY).setValue(ServerValue.TIMESTAMP)
}
}
Then I can simply create an instance of the POJO and call push() on it which properly populates the creation time property.
This definitely makes the POJO a little less plain and involves logic a POJO shouldn't know about. However using #Exclude annotations and/or casts as outlined in some of the responses here also requires knowledge of the storing mechanism.
Solution 2: Helper or DatabaseReference extension (Kotlin)
To overcome this you can of course also just create a pushTask(task: Task) method in a helper or - if using Kotlin - an extension method to e.g. DatabaseReference which could look like this:
fun DatabaseReference.push(pojo: Pojo) {
push()
.apply {
setValue(pojo)
child(Pojo.CREATED_AT_KEY).setValue(ServerValue.TIMESTAMP)
}
}
Looking at it now I come to think that I actually like the second approach more (if I have Kotlin at my disposal - I don't like helpers). But this is probably just a matter of taste. ;)
Currently, the Google's version of ServerValue.TIMESTAMP returns {".sv":"timestamp"} which is used as a directive for Firebase to fill that field with the server timestamp once you save the data to the Firebase server.
When you create your data on the client side however, you don't have the actual timestamp to play with yet (ie. use as the creation date). You only will have an access to the timestamp after the initial save and consequent retrieval, which - I imagine - is sometimes too late and not very elegant.
Before Google:
Update: Ignore this section as it is incorrect - I misunderstood the examples. ServerValue.TIMESTAMP always returned the {".sv":"timestamp"}.
As far as I understand in pre-google Firebase there seemed to be a server-generated timestamp available that allowed you to acquire the actual timestamp:
import com.firebase.client.ServerValue;
ServerValue.TIMESTAMP // eg. 1466094046
(ref 1, ref 2)
Questions:
Is such save/retrieval the only way to get the server-generated creation date on my model instances?
If yes can you propose a method of implementing such pattern?
Am I understanding correctly ServerValue.TIMESTAMP has changed with Google's acquisition of Firebase? Update: No, #FrankvanPuffelen replied that nothing's changed during acquisition.
Note:
I'm not considering using new Date() on client side as I've been reading it's not safe, though please share your thoughts if you think different.
When you use the ServerValue.TIMESTAMP constant in a write operation, you're saying that the Firebase Database server should determine the correct timestamp when it executes the write operation.
Let's say we run this code:
ref.addValueEventListener(new ValueEventListener() {
public void onDataChange(DataSnapshot dataSnapshot) {
System.out.println(dataSnapshot.getValue());
}
public void onCancelled(DatabaseError databaseError) { }
});
ref.setValue(ServerValue.TIMESTAMP);
This will execute as follows:
you attach a listener
you write a value with ServerValue.TIMESTAMP
the Firebase client immediate fires a value event with an approximation of the timestamp it will write on the server
your code prints that value
the write operation gets sent to the Firebase servers
the Firebase servers determine the actual timestamp and write the value to the database (assuming no security rules fail)
the Firebase server send the actual timestamp back to the client
the Firebase client raises a value event for the actual value
your code prints that value
If you're using ChildEventListener instead of a ValueEventListener, then the client will call onChildAdded in step 3 and onChildChanged in step 8.
Nothing changed in the way we generate the ServerValue.TIMESTAMP since Firebase joined Google. Code that worked before, will continue to work. That also means that the first answer you linked is a valid way to handle it.
I'm doing it a bit differently.
Solution 1: push() method in POJO
As I don't want to clutter my POJOs with strange getters or properties, I'm just defining a push() method inside my POJOs which looks like this:
/**
* Pushes a new instance to the DB.
*
* #param parentNode `DatabaseReference` to the parent node this object shall be attached to
*/
fun push(parentNode: DatabaseReference) {
parentNode
.push()
.apply {
setValue(this#Pojo)
child(Pojo.CREATED_AT_KEY).setValue(ServerValue.TIMESTAMP)
}
}
Then I can simply create an instance of the POJO and call push() on it which properly populates the creation time property.
This definitely makes the POJO a little less plain and involves logic a POJO shouldn't know about. However using #Exclude annotations and/or casts as outlined in some of the responses here also requires knowledge of the storing mechanism.
Solution 2: Helper or DatabaseReference extension (Kotlin)
To overcome this you can of course also just create a pushTask(task: Task) method in a helper or - if using Kotlin - an extension method to e.g. DatabaseReference which could look like this:
fun DatabaseReference.push(pojo: Pojo) {
push()
.apply {
setValue(pojo)
child(Pojo.CREATED_AT_KEY).setValue(ServerValue.TIMESTAMP)
}
}
Looking at it now I come to think that I actually like the second approach more (if I have Kotlin at my disposal - I don't like helpers). But this is probably just a matter of taste. ;)