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");
      }
    });

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");
      }
    });

• javascript
• firebase
• google-cloud-functions
• google-cloud-firestore

• post your code.. that helps us to help you with providing a better answer. Wele to SO and finish the tour ;-) – ZF007 Commented Jan 21, 2018 at 22:52
• For example: 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"); } }); – Fred Xie Commented Jan 21, 2018 at 23:19
• Please post it in your question with the correct formatting. Remove it from the ment as well. You can self edit..no problems with that ;-) – ZF007 Commented Jan 21, 2018 at 23:20

1 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");
    }
});