Firebase count num children of parent

Question

I\'m trying to get the number of children for a parent node in js firebase. I\'d like to have:

\'user\': {
    \'-Yuna99s993m\': { count: 1},
    \'-Yada99s9         


        

Answer 1

Calling event.data.ref.parent.numChildren() won't work, because parent is a DatabaseReference while numChildren() is defined on DataSnapshot (which you get by attaching a listener to a reference):

exports.setCount = functions.database.ref('/user/{userId}').onWrite(event => {
    return event.data.ref.parent.once("value", (snapshot) => {
      const count = snapshot.numChildren();
      return event.data.ref.update({ count });
    });
})

There is also a child-count example in the functions-samples Github repo that does precisely what you want: keeping a counter of the number of children. That example uses a more efficient approach for keeping the count.