如何获取Firestore文档中的字段？

Question

I am working on some Cloud functions that works with Firestore. I am trying to get a list of fields of a specific document. For example, I have a document reference from the even.data.ref , but I am not sure if the document contains the field I am looking at. I want to get a list of the fields' name, but I am not sure how to do it. I was trying to use Object.keys() method to get a list of keys of the data, but I only get a list of number (0, 1...), instead of name of fields.
I tried to use the documentSnapShot.contains() method, but it seems doesn't work.

exports.tryHasChild=functions.firestore.document('cities/{newCityId}')
.onWrite((event) =>{
  if (event.data.exists) {
    let myRef = event.data.ref;
    myRef.get().then(docSnapShot => {
      if (docSnapShot.contains('population')) {
        console.log("The edited document has a field of population");
      }
    });

Answer 1

As the documentation on using Cloud Firestore triggers for Cloud Functions shows, you get the data of the document with event.data.data() .

Then you can iterate over the field names with JavaScript's Object.keys() method or test if the data has a field with a simple array check:

exports.tryHasChild=functions.firestore.document('cities/{newCityId}')
.onWrite((event) =>{
  if (event.data.exists) {
    let data = event.data.data();
    Object.keys(data).forEach((name) => {
      console.log(name, data[name]);
    });
    if (data["population"]) {
      console.log("The edited document has a field of population");
    }
});