Update and delete data in Firebase

Question

This is my database:

{
  "UID1" : {
    "KEY" : {
      "Name" : "name1",
      "Email" : "[email protected]",
      "userid" : "UID1"
    }
  },
  "UID2" : {
    "KEY2" : {
      "Name" : "name1",
      "Email" : "[email protected]",
      "userid" : "UID2"
    },
    "KEY3" : {
      "Name" : "name2",
      "Email" : "[email protected]",
      "userid" : "UID2"
    },
    "KEY4" : {
      "Name" : "name3",
      "Email" : "[email protected]",
      "userid" : "UID2"
  }
}

I would like to update and delete data which for example would be at the position of "KEY2".

How can I achieve this? I have not yet tried any code in Android.

Answer 1

To write single data you can use the setValue() method on your DatabaseReference with your child Id's:

private void writeNewData(String userId, String name, String email) {
    User user = new User(name, email);    
    mDatabase.child("users").child(userId).setValue(user);
}

In your case you can do something like: mDatabase.child("UID2").child("KEY2").setValue(yourNewValueOrObject);

If you want to update a specific value, you should be more concise: mDatabase.child("UID2").child("KEY2").child("email").setValue(newEmail);

Anyway I recomend you to use custom classes as POJO's(Plain Old Java Object) with the values of each of your items in database. For example:

public class User {

    public String username;
    public String email;

    public User() {
        // Default constructor required for calls to DataSnapshot.getValue(User.class)
    }

    public User(String username, String email) {
        this.username = username;
        this.email = email;
    }

}

Finally to remove data you should use the removeValue() method in the same way.

  private void deleteUserData(String userId) {           
        mDatabase.child("users").child(userId).removeValue();
    }

This method will remove the whole reference from your Database, so be care with it. In the case that you wanted to remove a specific field, you should add another .child() call to the tree. For example, let's say that we want to remove the email value from "KEY2" node: mDatabase.child("users").child(userId).child("email").removeValue();

Finally, there's the case that maybe we want to update multiple fields in different database nodes. In that case we should use the updateChildren() method with a map of references and values.

private void writeNewPost(String userId, String username, String title, String body) {
   // Create new post at /user-posts/$userid/$postid and at
   // /posts/$postid simultaneously
   String key = mDatabase.child("posts").push().getKey();
   Post post = new Post(userId, username, title, body);
   Map<String, Object> postValues = post.toMap();

   Map<String, Object> childUpdates = new HashMap<>();
   childUpdates.put("/posts/" + key, postValues);
   childUpdates.put("/user-posts/" + userId + "/" + key, postValues);

   mDatabase.updateChildren(childUpdates);
}

What updateChildren method do. Is a setValue () call over each row in the given Map<String, Object> being the key the full reference of the node and the Object the value.

You can read more update and delete data in the official Firebase documentation