How to add multiple items to array in Firebase database in Java?

Question

In my Android Studio Java project, in Firebase Realtime database I am setting favorite foods to the user logged in. Everytime I use setValue, it overwrites the existing entry. I would like to add multiple foods such as in an array.

Here is the code below that is updating the Firebase Realtime database

    FirebaseAuth.getInstance().getCurrentUser();
    FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

    FirebaseDatabase database =  FirebaseDatabase.getInstance();

    String userId = user.getUid();
    User user1 = new User("banana");
    DatabaseReference mRef =  database.getReference().child("Users").child(userId);
    mRef.setValue(user1);

Here is the User java class

public class User {

    public String foods;

    //required default constructor
    public User() {
    }

    public User(String foods) {
        this.foods = foods;
    }

    public String getFoods() {
        return foods;
    }

    public void setFoods(String foods) {
        this.foods = foods;
    }
}

In Firebase this is an example of my JSON response:

{
  "Users" : {
    "ExampleUser1" : {
      "foods" : "banana"
    }
  }
}

Replacing

mRef.setValue(user1);

with

mRef.push().setValue(user1);

seems to get me where I need to go.

{
  "Users" : {
    "ExampleUser1" : {
      "-MZ4Cfec_EFb6i5bUIEl" : {
        "foods" : "banana"
      },
      "-MZ4EJV14CKUvYn9ISJl" : {
        "foods" : "apple"
      }
    }
  }
}

EDIT: This is the solutions I ended up using. Thank you all for your help and comments.

Arrays are not stored as array in the firebase realtime database Handling arrays with firebase realtime database is a bit tricky and they don’t work as expected. Firebase stores them as key value pair. To get the desired result, I used a hash map where I can set the key and value pair. This is the only code needed and I deleted the User class. The string fruit is an example and everytime it is updated, it was added to the database for that user. Duplicate entries are not allowed since I set the value of the fruit to equal the key as well.

    String fruit="banana"
    FirebaseAuth.getInstance().getCurrentUser();
    FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

    FirebaseDatabase database =  FirebaseDatabase.getInstance();

    String userId = user.getUid();
    DatabaseReference mRef =  database.getReference().child("Users").child(userId);

    Map<String, Object> updates = new HashMap<String,Object>();

    updates.put(fruit, fruit);

    mRef.updateChildren(updates);

Here is the JSON response from Firebase realtime database:

{
  "Users" : {
    "UserExample1" : {
      "banana" : "banana",
      "apple" : "apple",
      "orange" : "orange"
    }
  }
}

Answer 1

Arrays are not stored as array in the firebase realtime database Handling arrays with firebase realtime database is a bit tricky and they don’t work as expected. Firebase stores them as key value pair. To get the desired result, I used a hash map where I can set the key and value pair. This is the only code needed and I deleted the User class. The string fruit is an example and everytime it is updated, it was added to the database for that user. Duplicate entries are not allowed since I set the value of the fruit to equal the key as well.

    String fruit="banana"
    FirebaseAuth.getInstance().getCurrentUser();
    FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();

    FirebaseDatabase database =  FirebaseDatabase.getInstance();

    String userId = user.getUid();
    DatabaseReference mRef =  database.getReference().child("Users").child(userId);

    Map<String, Object> updates = new HashMap<String,Object>();

    updates.put(fruit, fruit);

    mRef.updateChildren(updates);

Here is the JSON response from Firebase realtime database:

{
  "Users" : {
    "UserExample1" : {
      "banana" : "banana",
      "apple" : "apple",
      "orange" : "orange"
    }
  }
}

Answer 2

If you want to store an array of foods, you should model that into your `` first.

public class User {

    public String[] foods;

    //required default constructor
    public User() {
    }

    public User(String[] foods) {
        this.foods = foods;
    }

    public String[] getFoods() {
        return foods;
    }

    public void setFoods(String[] foods) {
        this.foods = foods;
    }
}

Then you can simply set that array to the database:

String userId = user.getUid();
User user1 = new User(new String[] {"banana", "apple"});
DatabaseReference mRef = database.getReference().child("Users").child(userId);
mRef.setValue(user1);

I'd also recommend reading these, as arrays are a common antipattern in Firebase:

• Best Practices: Arrays in Firebase.
• Firebase query if child of child contains a value

Answer 3

try update() and see if it works