CODEWITHSUNDEEP
firebase
user9170
user9170

Reputation: 1000

Why do I get child_added event on remove?

The following code produces an endless loop of repeated child_added, though I never add a child. The nodes are removed. I just loop forever. How can I fix this?

//notifications branch is pre-populated when I get here:
notifications.startAt(null).on('child_added', processNotification, logError);

function processNotification(notification)
{
    removeNotification(notification);
}

function removeNotification(notification)
{
    var child = notifications.child(notification.name());
    console.log("REMOVING", child.toString());
    child.remove();     
}

What I log is the same four nodes (A,B,C,D) being removed:

REMOVING https://my.firebaseio.com/experimental/-JVMi0_4poXfOWUt5g49 - A
REMOVING https://my.firebaseio.com/experimental/-JVMi1Y_bFwZAkffRel4 - B
REMOVING https://my.firebaseio.com/experimental/-JVMi2lyhKj8z27ik71x - C
REMOVING https://my.firebaseio.com/experimental/-JVMhzazdgHYAstqxu8L - D
REMOVING https://my.firebaseio.com/experimental/-JVMi0_4poXfOWUt5g49 - A
REMOVING https://my.firebaseio.com/experimental/-JVMi1Y_bFwZAkffRel4 - B
REMOVING https://my.firebaseio.com/experimental/-JVMi2lyhKj8z27ik71x - C
REMOVING https://mu.firebaseio.com/experimental/-JVMhzazdgHYAstqxu8L - D
...

Upvotes: 0

Views: 1087

Answers (2)

user9170
user9170

Reputation: 1000

Ultimately, I just dropped the query and went with normal processing, dropping the "startAt(null)":

notifications.on('child_added', processNotification, logError);

It's not obvious that the behavior will be different from the documentation, but the startAt(null) does not produce the same behavior (though in thoery it should). I would love to see this better documented.

Upvotes: 1

Frank van Puffelen
Frank van Puffelen

Reputation: 599716

I was able to reproduce the problem. I think it is caused by the fact that the Query tries to keep items in its "window" when you remove one.

You can work around this problem by using a once('value' instead of on('child_added', like this:

notifications.startAt(null).once('value', processNotifications);

function processNotifications(notifications)
{
    notifications.forEach(function(notification) {
        notification.ref().remove();
    });
}

Since the value only fires once, it will not be interfering with the remove operation.

Upvotes: 1

Related Questions